Composite particle for electrode and method for producing same, electrode and method for producing same, and electrochemical device and method for producing same

ABSTRACT

Composite particles for an electrode of the invention are produced through a granulating step in which, a conductive additive and a binder are brought into a close contact with particles consisting of the electrode active material to integrate with each other. The granulating step preferably comprises a process for preparing a stock solution comprising the binder, the conductive additive and a solvent, a process for forming a fluidized bed by throwing particles of electrode active material into a fluidizing bathe and a process for bringing the particles of electrode active material and the particles of conductive additive into a close contact with the binder by spraying a stock solution into the fluidizing bathe, allowing the stock solution adhering to the particles of electrode active material and drying the same to remove the solvent from the adhered stock solution. Composite particles thus obtained are used as the constituent material for electrode, and further, the electrode is used as an anode and/or cathode of an electrochemical element; thereby, the internal resistance of electrode can be reduced satisfactorily and the power density of the electrochemical element can be increased satisfactorily.

TECHNICAL FIELD

The present invention relates to a composite particle for electrode,which is used as constituent material for electrode usable for anelectrochemical element such as a primary cell, a secondary cell(particularly, lithium ion secondary cell), an electrolytic cell, acapacitor (particularly, electrochemical capacitor) and producing methodthereof. Also, the invention relates to an electrode in which thecomposite particle for electrode is used as a constituent material andthe producing method thereof and an electrochemical element providedwith the electrode and producing method thereof.

BACKGROUND ART

Recently, potable equipments have been developed brilliantly. As a largedriving force, development of a high-energy cell such as a lithium ionsecondary cell, which are widely employed as a power source for suchequipments are given. Such high-energy cell comprises, principally, acathode, an anode and an electrolyte layer (for example, a layerconsisting of liquid electrolyte or solid electrolyte) disposed betweenthe cathode and the anode.

Electrochemical elements such as the high-energy batteries exemplifiedby the lithium ion secondary cell and electrochemical capacitorsexemplified by electric double layer capacitor are now under variousresearch and development for further increasing the characteristics torespond to the future development of equipments such as potableequipments in which electrochemical elements are provided. Particularly,it is desired to further improve the power density. And further, it isdesired to achieve an electrochemical element having superiorcharging/discharging characteristics capable of satisfactorilyresponding to sharp and, in particular, large changes of the loadrequirements of the equipment.

Conventionally, the cathode and/or anode are produced through thefollowing process; i.e., a coating liquid (for example, one in slurrystate or paste state) for forming an electrode, which comprises anelectrode active material, a binder (synthetic resin or the like), aconductive additive and a dispersion medium and/or a solvent, isprepared; and the coating liquid is applied to the surface of acollector (for example, metallic foil or the like), and then dried;thereby a layer comprising the electrode active material (referred to asan “active material-containing layer”) is formed on the surface of thecollector (for example, refer to Japanese Patent Application Laid-OpenNo. Hei 11-283615).

In this method (wet processing), the conductive additive may not beadded to the coating liquid. In place of the coating liquid, withoutusing the dispersion medium and solvent, sometimes a kneaded productcomprising an electrode active material, a binder and a conductiveadditive is prepared, and the product may be formed into a sheet-likeconfiguration using a heat roll pressing machine and/or a heat pressingmachine. Also, the coating liquid may be further added with conductivepolymer to form, so-called, “polymer electrode.” In the case where theelectrolyte layer is solid, a method, in which the coating liquid isapplied to the surface of the electrolyte layer, may be employed.

Further, in order to further improve the cell characteristics, forexample, the following positive electrode for lithium secondary cell andproducing method thereof has been proposed. That is, a compositeparticle comprising a manganese dioxide (active material for cathode)particle and carbon material powder fixed to the surface of themanganese dioxide particle (conductive additive) is used as theelectrode material for the cathode to prevent the charging/dischargingcapacity of cell from being reduced, which is caused from the cathode(for example, refer to Japanese Patent Application Laid-Open No. Hei2-262243).

Furthermore, in order to further increase the discharging characteristicand productivity or the like, the producing method of a positiveelectrode mix for an organic electrolyte cell has been proposed. Thatis, slurry comprising a positive electrode active material (activematerial for cathode), a conductive agent (conductive additive), abinder and a solvent, of which solid content is 20 to 50% by weight; andaverage particle diameter of the solid content is 10 μm or less, isprepared, and the slurry is granulated in a manner of spray dryingmethod (for example, refer to Japanese Patent Application Laid-Open No.2000-40504).

DISCLOSURE OF THE INVENTION

However, the lithium ion secondary cell equipped with an electrode,which was produced in a manner of wet processing of the art disclosed,for example, in the above-described Japanese Patent ApplicationLaid-Open No. Hei 11-283615, had the following problem. There is a limitto increase the power density of the cell; and particularly, when thecell was used under operation conditions such that the load requirementschanges sharply and, in particular, largely, it was extremely difficultto form a cell, which had superior charging/discharging characteristicscapable of satisfactorily responding to such load requirements.

That is, to further increase the output of the cell, when the thicknessof the active material-containing layer for electrode is made thinner,since the internal resistance (impedance) of the entire activematerial-containing layer can be reduced, it is possible to achieve theabove intension. However, in this case, the content of the activematerial is short, and accordingly, the cell capacity and the energydensity of the cell is hardly ensured satisfactorily. Since thecollector and the separator do not contribute to the cell capacity, fromthis viewpoint also, the cell capacity is hardly ensured satisfactorily.

Further, the inventors found the following fact. That is, the compositeparticle disclosed in Japanese Patent Application Laid-Open No. Hei2-262243 is insufficient in mechanical strength. Therefore, carbonmaterial powder fixed to the surface of the manganese dioxide particlepeels off easily during forming of the electrode. Satisfactorydispersion of the carbon material powder within the obtained electrodetends to be insufficient. Therefore, the desired improvement of theelectrode characteristics and further increase of the output of cell arehardly obtained reliably or satisfactorily.

Further, a positive electrode mix for an organic electrolyte celldisclosed in Japanese Patent Application Laid-Open No. 2000-40504 isproduced in the following manner. That is, slurry containing a solventis sprayed and dried in a hot air to form cluster (composite particles)comprising a positive electrode active material, a conductive agent anda binder. Here, the inventors found the following fact. That is, in thiscase, the process of dry and solidification advances in a state that thepositive electrode active material, the conductive agent and the binderare dispersed in a solvent. Therefore, since agglomeration of the binderitself and agglomeration of the conductive agent advance during thedrying process, and the conductive agent and the binder failed inestablishing a close contact with the surface of each particleconsisting of the positive electrode active material constituting theobtained cluster (composite particles) in a state that an effectiveconductive network is established respectively being dispersedsatisfactorily. Therefore, it is difficult to further increase theoutput of the cell reliably and satisfactorily.

In particular, the inventors found the following fact; i.e., in the artdisclosed in Japanese Patent Application Laid-Open No. 2000-40504, asshown in FIG. 22, among the respective particles consisting of positiveelectrode active material constituting obtained cluster (compositeparticles) P100, there are many clusters P11, which are enclosed only bya large agglomerate P33 of binder, being electrically isolated, andaccordingly, not being utilized, in the clusters (composite particles)P100. Also, the inventors found the following fact. That is, whenparticles consisting of the conductive agent form an agglomerate duringdrying process, the particles consisting of the conductive agent areunevenly distributed into an agglomerate P22 within the obtained cluster(composite particles) P100. Thus conduction paths for the electron(electron conduction network) are not established satisfactorily in thecluster (composite particles) P100. Therefore, the electron conductivitycannot be obtained satisfactorily. Further, the inventors found thefollowing fact. That is, the large agglomerate P33 consisting of abinder only encloses the agglomerate P22 of particles consisting of theconductive agent while electrically isolating the particles. In thisviewpoint also, conduction path for the electron (electron conductionnetwork) is not established satisfactory in the cluster (compositeparticles) P100 failing in obtaining the electron conductivitysatisfactorily.

Further, the inventors found the following fact. That is, in theconventional electrodes such as composite particles disclosed in theabove-described Japanese Patent Application Laid-Open No. Hei 2-262243and Japanese Patent Application Laid-Open No. 2000-40504, in order toensure the stability of configuration of the electrode, a large amountof binder (binder), of which insulation performance or electronconductivity is low, is used along with the electrode active materialand the conductive additive. Therefore, in this viewpoint also, theelectron conductivity of the electrode is not ensured satisfactorily.Also, in the case where the electrode is produced using the compositeparticles disclosed in the above-described Japanese Patent ApplicationLaid-Open No. Hei 2-262243 and Japanese Patent Application Laid-Open No.2000-40504, since the binder is used, the above-described problemsoccur.

In a primary cell and a secondary cell also, which are another type ofthe above-described lithium ion secondary cell, in the case of the cell,which has the electrode produced in the above-described conventionalordinary producing method (wet processing), i.e., a method, which usesthe coating liquid comprising at least the electrode active material,the conductive additive and the binder, there resides the same problemas described above.

Further, in an electrolytic cell and capacitor (for example, anelectrochemical capacitor such as an electric double layer capacitor)having the electrode produced in a method, which uses, in place of theelectrode active material in the cell, an electron conductive material(carbon material or metal oxide) as the electrode active material andslurry comprising at least the conductive additive and the binder, thereresides the same problem as described above.

The invention has been proposed in view of the problems residing in theabove-described conventional arts. An object of the invention is toprovide a composite particle for electrode, which is, even when thebinder is used as the constituent material of electrode, capable ofeasily and reliably forming the electrode having superior electrodecharacteristics. Another object of the invention is to provide anelectrode, which comprises the composite particle for electrode as theconstituent material of which internal resistance is satisfactorilyreduced, and has superior electrode characteristics capable of easilyincreasing the power density of the electrochemical elementsatisfactorily, as well as, to provide an electrochemical element, whichis provided with such electrode and has superior charging anddischarging characteristics capable of, even when the load requirementschange sharply and, in particular, largely, responding theretosatisfactorily. Further another object of the invention is to provide aproducing method for easily and reliably obtaining the above-describedcomposite particle for electrode, electrode and electrochemical elementrespectively.

The inventors intensively studied to achieve the above objects. As aresult, the following fact was found. That is, to form an electrode, theconventional electrode forming method employs a method which uses acoating liquid or a kneaded product comprising at least theabove-described electrode active material, conductive additive andbinder. Therefore, the electrode active material, conductive additiveand binder in the active material-containing layer of the obtainedelectrode are dispersed unevenly. This fact largely affects to cause theabove-described problems.

That is, in the conventional methods, in which a coating liquid or akneaded product is used like the arts disclosed in Japanese PatentApplication Laid-Open No. Hei 11-283615 and Japanese Patent ApplicationLaid-Open No. Hei 2-262243, a coating liquid or a kneaded product isapplied to the surface of the collector to form a coating of the coatingliquid or the kneaded product on the surface, and then the coating isdried to remove the solvent; thereby the active material-containinglayer is formed. The inventors found the following fact. That is, in thedrying process of the coating, the conductive additive and binder withsmall specific gravity float up to the adjacent of the coating surface.As a result, the following state was found. That is, a state ofdispersion of the electrode active material, the conductive additive andbinder in the coating failed to establish an effective conductivenetwork; for example, the state of dispersion was uneven; close contactamong the electrode active material, conductive additive and binder wasnot satisfactorily established; and in the obtained activematerial-containing layer, the conduction path for the electron was notestablished satisfactorily; accordingly, the resistivity and the chargetransfer overvoltage of the active material-containing layer was notreduced satisfactorily.

Further, the following fact was found. That is, in the conventionalmethod for granulating slurry into the composite particle by means ofspray drying as disclosed, for example, in Japanese Patent ApplicationLaid-Open No. 2000-40504, a positive electrode active material (activematerial for cathode), a conductive agent (conductive additive) and abinder are comprised in the same slurry. In this case, the state ofdispersion of the electrode active material, the conductive additive andthe binder in the obtained granulated matter (composite particles)depends on the state of dispersion of the electrode active material, theconductive additive and the binder in the slurry (particularly, thestate of dispersion of the electrode active material, the conductiveadditive and the binder during the process that drop of the slurry isdried). Therefore, as previously described referring to FIG. 22,agglomeration and uneven distribution of the binder, and agglomerationand uneven distribution of the conductive additive occur. As a result,the following state is resulted in. That is, an effective conductivenetwork is not established among the dispersed electrode activematerial, the conductive additive and the binder in the obtainedgranulated matter (composite particles). For example, due to unevendispersion of the electrode active material, the conductive additive andthe binder, the close contact among these is not satisfactorilyestablished; thus, the electron conduction path is not satisfactorilyestablished in the obtained active material-containing layer.

Further, the inventors found the following fact. That is, in the abovecase, the conductive additive and the binder can not be selectively andsatisfactorily dispersed on the surface of the electrode activematerial, which can come into contact with the electrolyte andparticipate in the reaction of the electrode. And, there reside suchuseless conductive additives that do not contribute to establishingelectron conduction network for effectively conducting the electrongenerated in the reaction field: and there reside such useless bindersthat contribute to just increasing the electric resistance.

Further, the inventors found the following fact. That is, in suchconventional art as composite particles disclosed in Japanese PatentApplication Laid-Open No. Hei 2-262243 and Japanese Patent ApplicationLaid-Open No. 2000-40504, since the state of dispersion of the electrodeactive material, the conductive additive and the binder in the coatingis uneven, the close contact of the electrode active material and theconductive additive with the collector was not establishedsatisfactorily. Particularly, such problem that the state of dispersionof the electrode active material, the conductive additive and the binderin the coating and the electrode obtained thereby is uneven, and theproblem that these components are distributed unevenly in the electroderespectively appears considerably when the thickness of the electrode isincreased.

It is generally understood among the persons skilled in the art that,when the binder is used, the internal resistance of the electrode tendsto increase. However, the inventors found the following fact andachieved the present invention. That is, when a particle comprising theelectrode active material, the conductive additive and the binder ispreviously formed by means of granulating step, which will be describedbelow, and when the active material-containing layer for electrode isformed using the particle as the constituent material, even when thebinder is comprised therein, an active material-containing layer, whichhas the resistivity value (or, internal resistance value after beingnormalized with superficial volume) satisfactorily lower than that ofthe electrode active material itself, can be formed.

That is, the invention provides a composite particle for electrodecomprising an electrode active material, a conductive additive havingelectron conductivity and a binder capable of binding the electrodeactive material and the conductive additive, the composite particle forelectrode being formed through a granulating step in which theconductive additive and the binder are brought into a close contact withthe particle consisting of the electrode active material and integratedwith each other, and the granulating step comprising:

a stock solution preparing step for preparing a stock solutioncomprising the binder, the conductive additive and a solvent;

a fluidized bed forming step for forming the particle consisting of theelectrode active material into a fluidized bed by throwing the particleconsisting of the electrode active material into a fluidizing bathe; and

a spray-drying step, in which the stock solution is sprayed into thefluidized bed comprising the particle consisting of the electrode activematerial, thereby the stock solution is allowed adhering to the particleconsisting of the electrode active material and dried to remove thesolvent from the stock solution adhered to the surface of the particleconsisting of the electrode active material to bring the particleconsisting of the electrode active material and the particle consistingof the conductive additive into a close contact with each other by meansof the binder.

In this invention, the wording “electrode active material”, which servesas the constituent material of the composite particle for electrode,means the following substances depending on the electrode to be formed.That is, in the case of an electrode where the electrode to be formed isused as the anode of a primary cell, the wording “electrode activematerial” means a reducing agent; and in the case of a cathode of aprimary cell, the wording “electrode active material” means an oxidizingagent. In the “particle consisting of the electrode active material”, asubstance other than the electrode active material may be comprised toan extent that the function of the invention (function of the electrodeactive material) is not reduced.

Further, in the case where the electrode to be formed is an anode, whichis used in a secondary cell (at discharging), the wording “electrodeactive material” means a reducing agent, which is a substance capable ofexisting chemically stably in any of reductant state and oxidant state;and capable of acting reversibly in any of the reductive reaction froman oxidant to a reductant, and the oxidative reaction from the reductantto the oxidant. Further, in the case where the electrode to be formed isa cathode (at discharging), which is used in a secondary cell, thewording “electrode active material” means an oxidizing agent, which is asubstance capable of, in any state of reductant and oxidant, existingchemically stably; and capable of reversibly acting any of reductivereaction from oxidant to reductant and oxidative reaction from reductantto oxidant.

Also, in addition to the above, in the case where the electrode to beformed is an electrode, which is used in a primary cell and a secondarycell, the “electrode active material” may be a material capable ofstoring or releasing a metal ion, which participates in the electrodereaction (intercalate, or doping/dedoping). As for this material, forexample, a carbon material, a metal oxide (comprising a composite metaloxide) or the like, which are used for the anode and/or cathode of alithium ion secondary cell, are mentioned.

In this description, as a matter of convenience, the electrode activematerial for the anode will be referred to as an “anode activematerial”; and the electrode active material for the cathode will bereferred to as a “cathode active material.” In this case, the wording“anode” in the expression of “anode active material” will be used on thebasis of the polarity when the cell is discharged (negative electrodeactive material); and the wording “cathode” in the expression of“cathode active material” will be used on the basis of the polarity whenthe cell is discharged (positive electrode active material). Particularexamples of the anode active material and the cathode active materialwill be given later.

Also, in the case where the electrode to be formed is an electrode usedfor an electrolytic cell or an electrode used for a capacitor(condenser), the wording “electrode active material” means a metal(comprising metal alloy), a metal oxide or a carbon material having theelectron conductivity.

In the above-described granulating step, a fine drop of the stocksolution, which comprises the conductive additive and the binder, issprayed directly to the particle consisting of the electrode activematerial in the fluidizing bathe. Therefore, compared to the case of theabove-described conventional forming methods of the composite particle,the respective constituent particles constituting the composite particlecan be satisfactorily prevented from advance of agglomeration. As aresult, the respective constituent particles in the obtained compositeparticles can be satisfactorily prevented from being unevenlydistributed. Further, the conductive additive and the binder can beselectively and satisfactorily dispersed on the surface of the electrodeactive material, which can come into contact with the electrolyte andparticipate in the reaction of the electrode.

Therefore, the composite particles for electrode in accordance with theinvention are brought into a close contact with each other, in a statein which each of these has been extremely satisfactorily dispersed.Also, in the composite particle for electrode in accordance with theinvention, the particle size thereof can be controlled, by controllingthe temperature in the fluidizing bathe, the spray amount of the stocksolution to be sprayed into the fluidized bed, the amount of electrodeactive material to be thrown into the airflow generated in thefluidizing bathe, the speed of the airflow generated in the fluidizingbathe, the type of the flow (circulation) of the airflow (laminar flow,turbulent flow etc) or the like in the granulating step. The compositeparticle for electrode is used as the constituent material of a coatingliquid or a kneaded product for producing the electrode.

Thus, in the above-described granulating step, the drop of raw materialcomprising the conductive additive and the like is directly sprayed tothe flown particles. Therefore, the flowing method of the particle isnot particularly limited. For example, a fluidizing bathe in whichairflow is generate and the particle is flown by the airflow, afluidizing bathe in which the particle is rotated and flown by astirring blade, a fluidizing bathe in which the particle is flown bymeans of the vibration or the like may be employed. In the producingmethod of the composite particle for electrode, in order to evenly formthe configuration and size of the obtained composite particle, it ispreferred that, in the fluidized bed forming step, the airflow isgenerated in the fluidizing bathe, the particle consisting of theelectrode active material is thrown into the airflow and the particleconsisting of the electrode active material is formed into a fluidizedbed.

Within the composite particle for electrode, the electron conductionpath (electron conduction network) is established extremelysatisfactorily in three dimensionally. In the structure of the electronconduction path, even after the coating liquid or the kneaded productwhich comprises the particle is prepared, by controlling the preparingconditions (for example, selection of the dispersion medium or thesolvent, or the like when preparing the coating liquid), substantiallyinitial state thereof can be easily maintained.

Therefore, in the process, in which the liquid film of coating liquid orthe kneaded product comprising the composite particle for electrode isformed on the surface of collector member, and then, the liquid film issolidified (a process, for example, drying the liquid film or the like),unlike the conventional method, the close contact among the conductiveadditive, the electrode active material and the binder can besatisfactorily prevented from reducing, and the close contact of theconductive additive and the electrode active material with the surfaceof collector member can be satisfactorily prevented from reducing.

The inventors understand the reason of the above as described below.That is, in the active material-containing layer for electrode obtainedin accordance with the invention, compared to the conventionalelectrodes, the electron conduction path (electron conduction network)is established extremely satisfactorily in three-dimension.

Further, even when the active material-containing layer for electrode isformed relatively thick (for example, 150 μm or more), by using thecomposite particle for electrode in accordance with the invention, theelectrode characteristics superior to the conventional can be obtained.That is, the energy density per capacity of the electrochemical elementsuch as cell can be increased easily and reliably. Further, even whenthe active material-containing layer for electrode is formedcomparatively thin (for example, 100 μm or less), since an electrodewith low internal resistance can be formed by using the compositeparticle for electrode in accordance with the invention, which hassuperior electron conductivity, the electrochemical element equippedwith the electrode enables the charging and discharging (when theelectrochemical element is a primary cell, discharge only) swift andsatisfactory repeatability at a current density comparatively higherthan the conventional electrodes (for example, when the thickness of theactive material-containing layer is 100 μm, 3 mA/cm² or more).

Extremely satisfactory ion conduction path can be established easily inthe active material-containing layer for electrode also by carrying outany one of the following techniques. That is, (A) when producing thecomposite particle for electrode, a conductive polymer, which has theion conductivity, is further added as the constituent material; (B) whenpreparing a coating liquid or a kneaded product for forming anelectrode, a conductive polymer having the ion conductivity is added asthe constituent other than the composite particle for electrode; and (C)a conductive polymer having the ion conductivity is added to both of thecomposite particle for electrode as the constituent material thereof,and a coating liquid or kneaded product for forming electrode as theconstituent thereof.

When a conductive polymer having the ion conductivity can be used as thebinder to be the constituent material of the composite particle forelectrode, the conductive polymer having the ion conductivity may beused. It is understood that the binder having the ion conductivity alsocontributes to establishing the ion conduction path in the activematerial-containing layer. By using the composite particle forelectrode, the above-described polymer electrode can be formed. Further,as the binder, which will be the constituent material of the compositeparticle for electrode, a polymer electrolyte having the electronconductivity may be used.

By employing the above-described constitution, in this invention, theelectrode, which has the electron conductivity and the ion conductivitysuperior to the conventional electrodes, can be formed easily andreliably. In the electrode formed using the composite particle forelectrode in accordance with the invention, the contact boundary amongthe conductive additive, the electrode active material and theelectrolyte (solid electrolyte or liquid electrolyte), which serves asthe reaction field of the charge transfer reaction advancing in theactive material-containing layer, is formed three dimensionally in asatisfactory size; and also, the electrical contact state between theactive material-containing layer and the collector member is in anextremely satisfactory state.

Further, according to the invention, the composite particle forelectrode in a state extremely satisfactory dispersion of each of theconductive additive, the electrode active material and the binder ispreviously formed. Therefore, the addition amount of the conductiveadditive and the binder can be more satisfactorily reduced than theconventional particles.

In the invention, when a conductive polymer is used, the conductivepolymer may be of the kind same as or different from the conductivepolymers which serve as the constituent element of the above-describedcomposite particle for electrode.

Further, in the invention, the electrode active material may be anactive material which can be used for the cathode of a primary cell or asecondary cell. Also, in the invention, the electrode active materialmay be an active material which can be used for the anode of the primarycell or the secondary cell. Further, in the invention, the electrodeactive material may be a carbon material or a metal oxide which has theelectron conductivity usable for the electrode constituting theelectrolytic cell or capacitor. In the invention, the electrolytic cellor capacitor represents an electrolytic cell that is provided with atleast a first electrode (anode), a second electrode (cathode) and anelectrolyte layer having the ion conductivity, and an electrochemicalcell, of which the first electrode (anode) and second electrode(cathode) are disposed opposite to each other being interposed by theelectrolyte layer. In this description, the wording “capacitor” is theidentical to the wording “condenser.”

By providing the electrode comprising the composite particle forelectrode to at least either one of the anode or cathode, preferably toboth thereof, an electrochemical element, which is capable of obtainingsuperior charging/discharging characteristics, can be structured easilyand reliably.

Further, the invention provides an electrode comprising at least aconductive active material-containing layer comprising, as thestructural material, composite particles composed of an electrode activematerial, a conductive additive having electron conductivity, and abinder capable of binding the electrode active material and theconductive additive, and a current collector situated in electricalcontact with the active material-containing layer,

the composite particle being formed through a granulating step in whichthe conductive additive and the binder are brought into a close contactwith the particle consisting of the electrode active material andintegrated with each other, and

the electrode active material and the conductive additive beingnon-isolated and electrically linked with each other in the activematerial-containing layer.

Compared to the conventional electrodes, in the electrode in accordancewith the invention, the resistivity and the charge transfer overvoltageof the active material-containing layer are satisfactorily reduced.Therefore, the power density of the electrochemical element can besatisfactorily increased easily and reliably.

The composite particle used for the electrode in accordance with theinvention is a particle, in which the conductive additive, the electrodeactive material and the binder are brought into a close contact witheach other, in a state in which each of these has been extremelysatisfactorily dispersed. The composite particle is used as maincomponent of fine particles for producing the active material-containinglayer for electrode by means of the dry method, which will be describedlater; or used as the constituent material of the coating liquid orkneaded product for producing the active material-containing layer forelectrode by means of the wet processing, which will be described later.

In the composite particle, an extremely satisfactory electron conductionpath (electron conduction network) is established three-dimensionally.When used as the main component of fine particles for producing theactive material-containing layer for electrode by means of the drymethod, which will be described later, even after forming the activematerial-containing layer by means of the heat treatment, the structureof the electron conduction path can be maintained in substantiallyinitial state. Also, when used as the constituent material of thecoating liquid or kneaded product for producing the activematerial-containing layer for electrode by means of the wet processing,which will be described later, even after preparing the coating liquidor kneaded product comprising the composite particle, by controlling thepreparing conditions (for example, selection of a dispersion medium orsolvent for preparing the coating liquid, or the like), the structure ofthe electron conduction path can be easily maintained in substantiallyinitial state.

That is, the electrode in accordance with the invention is formed in astate in which the above-described structure of the composite particleis maintained. Therefore, in the active material-containing layer, theelectrode active material and the conductive additive are electricallybound to each other without being isolated from each other. Therefore,in the active material-containing layer, an extremely satisfactoryelectron conduction path (electron conduction network) is establishedthree-dimensionally. Here, the wording “in the activematerial-containing layer, the electrode active material and theconductive additive are electrically bound to each other without beingisolated from each other” means the state that, in the activematerial-containing layer, the particle consisting of the electrodeactive material (or agglomerate thereof) and the particle consisting ofthe conductive additive (or agglomerate thereof) are electrically boundto each other “substantially” without being isolated from each other. Inparticular, it does not mean such a sate that all of the particlesconsisting of the electrode active material (or agglomerate thereof) andthe particle consisting of the conductive additive are electricallybound to each other without utterly isolated from each other, but meanssuch a state that the both are electrically satisfactorily bound to eachother in a range that the electric resistance of a level in which theeffect of this invention can be obtained.

The state of “in the active material-containing layer, the electrodeactive material and the conductive additive are bound electrically toeach other without being isolated from each other” can be confirmed bymeans of an SEM (Scanning Electron Micro Scope) photograph, TEM(Transmission Electron Microscope) photograph and EDX (Energy DispersiveX-ray Fluorescence Spectrometer) analysis data of sections of the activematerial-containing layer for electrode in accordance with theinvention. Also, by comparing SEM photograph, TEM photograph and EDXanalysis data of sections of the active material-containing layer to SEMphotograph, TEM photograph and EDX analysis data of the conventionalelectrodes, the electrode in accordance with the invention can beapparently distinguished from the conventional electrodes.

In the electrode in accordance with the invention, the granulating steppreferably comprises:

a stock solution preparing step for preparing a stock solutioncomprising the binder, the conductive additive and a solvent;

a fluidized bed forming step for forming the particle consisting of theelectrode active material into a fluidized bed by throwing the particleconsisting of the electrode active material into a fluidizing bathe; and

a spray-drying step, in which the stock solution is sprayed into thefluidized bed comprising the particle consisting of the electrode activematerial, thereby the stock solution is allowed adhering to the particleconsisting of the electrode active material and dried to remove thesolvent from the stock solution adhered to the surface of the particleconsisting of the electrode active material to bring the particleconsisting of the electrode active material and the particle consistingof the conductive additive into a close contact with each other by meansof the binder.

By employing the granulating step arranged as described above, theabove-described composite particle can be produced more reliably, and asa result, the effect of the invention can be obtained more reliably. Inthis granulating step, within the fluidizing bathe, fine drop of thestock solution comprising the conductive additive and the binder isdirectly sprayed to the particle consisting of the electrode activematerial. Therefore, compared to the above-described conventionalproducing method of the composite particles, the agglomeration of therespective constituent particles constituting the composite particle canbe satisfactorily prevented from advancing. As a result, each of theconstituent particles in the obtained composite particle can besatisfactorily prevented from being unevenly distributed. Further, theconductive additive and the binder are allowed dispersing selectivelyand satisfactorily to the surface of the electrode active material whichcan be brought into contact with the electrolyte and participate in theelectrode reaction.

Accordingly, the obtained composite particle becomes such particles thatthe conductive additive, the electrode active material and the binderare brought into a close contact with each other, in a state in whicheach of these has been extremely satisfactorily dispersed. Further, theparticle size of the composite particle can be controlled by, in thegranulating step, controlling the temperature in the fluidizing bathe,the amount of the stock solution to be sprayed in the fluidizing bathe,the amount of the electrode active material thrown into the airflowgenerated within the fluidizing bathe, the speed of the airflowgenerated within the fluidizing bathe and, type of the flow(circulation) of the airflow (laminar flow, turbulent flow etc) or thelike.

In the composite particle produced in the granulating step as describedabove, an extremely satisfactory electron conduction path (electronconduction network) is established three-dimensionally and morereliably. And in this case also, when used as the main component of fineparticles for producing the active material-containing layer forelectrode by means of the dry method, which will be described later,even after forming the active material-containing layer by means of theheat treatment, the structure of the electron conduction path can bemaintained in substantially initial state. Also, when used as theconstituent material of the coating liquid or kneaded product forproducing the active material-containing layer for electrode by means ofthe wet processing, which will be described later, even after preparingthe coating liquid or kneaded product comprising the composite particle,by controlling the preparing conditions (for example, selection of adispersion medium or a solvent for preparing the coating liquid, or thelike), the structure of the electron conduction path can be easilymaintained in substantially initial state.

Therefore, when the composite particle is used as the main component offine particles for producing the active material-containing layer forelectrode by means of the dry method, which will be described later,unlike the conventional conductive additive, the close contact betweenthe electrode active material and the binder and the close contact ofthe conductive additive and the electrode active material with thesurface of the collector can be satisfactorily prevented fromdecreasing.

Also, when the active material-containing layer for electrode is formedby means of wet processing, which will be described later, in theprocess in which the liquid film of coating liquid or kneaded productcomprising the composite particle is formed on the surface of thecollector, and then, the liquid film is solidified (for example, processto dry the liquid film, etc), unlike the conventional methods, the closecontact among the conductive additive, the electrode active material andthe binder and the close contact of the conductive additive and theelectrode active material with the surface of the collector can besatisfactorily prevented from decreasing.

The inventors understand the reason of the above. That is, as a resultof the above, in the active material-containing layer for electrode inaccordance with the invention, compared to the conventional electrode,an extremely satisfactory electron conduction path (electron conductionnetwork) is established three-dimensionally, the resistivity and thecharge transfer overvoltage of the active material-containing layer canbe largely reduced.

Further, even when the active material-containing layer for electrode isformed comparatively thinly (for example, 100 μm or less), by using theabove-described composite particles having superior electronconductivity, an electrode of which internal resistance (impedance) islow can be formed. The electrochemical element provided with thiselectrode can charge and discharge (when the electrochemical element isa primary cell, discharge only) with swift and satisfactoryrepeatability at a current density comparatively higher than theconventional (for example, when the thickness of the activematerial-containing layer is 100 μm, 3 mA/cm² or more). Thus, a higheroutput can be achieved easily.

In this case, in order to reliably increase the output of theelectrochemical element, the thickness T of the activematerial-containing layer and average particle diameter d of compositeparticles comprised in the active material-containing layer preferablysatisfy the conditions expressed by following formulas (1) to (3):0.0005≦(T/d)≦1  (1)1 μm≦T≦150 μm  (2)1 μm≦d≦2000 μm  (3).

If the conditions of the formulas (1) to (3) are not satisfiedsimultaneously, the following tendency appears largely. That is, when(T/d) in the formula (1) is smaller than 0.0005, the following tendencylargely appears. That is, the pressure for extending the layer of thecomposite particle sprayed (disposed) on the collector to form theactive material-containing layer by applying pressure becomes higher.The above-described satisfactory electron conduction network in thecomposite particle is hardly maintained.

When (T/d) of the formula (1) exceeds 1, the following tendency appearslargely. That is, in the active material-containing layer, a state inwhich plural composite particles are piled up in line in the directionof the normal line of the collector is formed. The contact boundary isformed between the composite particles. Since the boundary resistance(electric resistance) between the composite particles is larger than theinternal resistance in the composite particle, satisfactory outputcharacteristics are hardly obtained.

Further, when T in the formula (2) is smaller than 1 μm, the followingtendency appears largely. That is, since mechanical strength of theactive material-containing layer is not satisfactory, satisfactoryhandling performance is hardly obtained. Further, when T in the formula(2) exceeds 150 μm, the following tendency appears largely. That is, thedistance between the upper portion of the active material-containinglayer (adjacent portion of the surface opposite to the surface whichcontact with the collector) and the collector becomes too largeresulting in a longer charge transfer path. Thus, satisfactory outputcharacteristics are hardly obtained.

Further, when d in the formula (3) is smaller than 1 μm, the followingtendency appears largely. That is, particles (particles consisting ofthe electrode active material, etc), which serve as the core forproducing the composite particle, become too small; thus thesatisfactory compounds are hardly produced. When the granulating step iscarried out using the fluidizing bathe as described above, the followingtendency appears largely. That is, particles to be cores within thefluidizing bathe agglutinate; and thus, stable fluidized bed is hardlyformed. Further, when d in the formula (3) exceeds 2 mm, for theparticles to be cores for producing the composite particle, particleswith a large particle diameter have to be used. In this case, since theion diffusion speed within the particles with a large particle diameteris large, such tendency appears largely; i.e., satisfactory outputcharacteristics are hardly obtained.

The electrode in accordance with the invention may be characterized inthat a conductive polymer is further comprised in the activematerial-containing layer. Owing to this, the above-described polymerelectrode can be formed. In this case, the conductive polymer may becharacterized by being a conductive polymer having the ion conductivity,or being a conductive polymer having the electron conductivity. Also, asthe conductive polymer, a conductive polymer having the ion conductivityand a conductive polymer having the electron conductivity may be usedsimultaneously.

By adapting as described above, in accordance with the invention, theelectrode, which has the electron conductivity and the ion conductivitysuperior to the conventional electrodes, can be formed easily andreliably. When the composite particle is used as the main component offine particles for forming the active material-containing layer forelectrode by means of the dry method, which will be described later, theconductive polymer can be comprised in the active material-containinglayer by adding as the constituent other than the composite particleinto the fine particles. Also, when preparing the coating liquid forforming an electrode or the kneaded product for forming electrode, aconductive polymer can be comprised in the active material-containinglayer by adding the conductive polymer as the constituent other than thecomposite particle.

Further, in the electrode in accordance with the invention, when formingthe composite particle, a conductive polymer may be further added as theconstituent material. That is, the composite particle may becharacterized in that a conductive polymer is further comprised. In thiscase also, the conductive polymer may be characterized by being aconductive polymer having the ion conductivity, or being a conductivepolymer having the electron conductivity. Also, as the conductivepolymer, a conductive polymer having the ion conductivity and aconductive polymer having the electron conductivity may be usedsimultaneously.

As described above, by forming the active material-containing layerusing the composite particle comprising the conductive polymer, anextremely satisfactory ion conduction path and/or electron conductionpath can be established easily in the active material-containing layerfor electrode. The conductive polymer may be comprised in the compositeparticle by adding further as the constituent material when forming thecomposite particle.

In the electrode in accordance with the invention, when a conductivepolymer can be used as the binder, which serves as the constituentmaterial of the composite particle, the conductive polymer having theion conductivity may be used. That is, the invention may becharacterized in that the binder consists of a conductive polymer. It isunderstood that the binder having the ion conductivity contributes toestablishing an ion conduction path in the active material-containinglayer; and the binder having the electron conductivity contributes toestablishing an electron conduction path in the activematerial-containing layer.

The conductive polymer may be added to any of the followings; i.e., theconstituent material of the composite particle, the constituent of thefine particles (dry method) for forming electrode, the constituent ofthe coating liquid for forming an electrode (wet processing) and theconstituent of kneaded product (wet processing) for forming electrode.In this case also, an extremely satisfactory ion conduction path can beestablished easily in the active material-containing layer forelectrode.

In the electrode formed using the composite particle, contact boundaryamong the conductive additive, the electrode active material and theelectrolyte (solid electrolyte or liquid electrolyte), which serves asthe reaction field of the electron transfer reaction advancing withinthe active material-containing layer, is formed three-dimensionally in asatisfactory size. The state of electrical contact between the activematerial-containing layer and the collector is also in an extremelysatisfactory state.

Further, in the invention, the composite particle, of which state ofdispersion of the conductive additive, the electrode active material andthe binder is extremely satisfactory respectively, is previously formed.Therefore, compared to the conventional composite particles, the amountof the conductive additive and the binder to be added can besatisfactorily reduced.

In the electrode in accordance with the invention, when a conductivepolymer is used, the conductive polymer may be of the type same as ordifferent from the conductive polymers which serve as the constituentelement of the above-described composite particles.

Further, in the electrode in accordance with the invention, theelectrode active material may be an active material, which can be usedfor the cathode of the primary cell or the secondary cell. In thisinvention, the electrode active material may be an active material,which can be used for the anode of the primary cell or the secondarycell. Further, in the invention, the electrode active material may be acarbon material or metal oxide having the electron conductivity, whichis usable for the electrode constituting the electrolytic cell or thecapacitor.

The invention provides an electrochemical element comprising at least ananode, a cathode and an electrolyte layer having the ion conductivity,the element having a structure such that the anode and the cathode aredisposed opposite to each other being interposed by an electrolytelayer,

any one of the electrode of the above-described inventions beingprovided as the electrode of one or both of the anode and the cathode.

By providing the electrode in accordance with the invention providedwith the active material-containing layer comprising the compositeparticle to at least one or preferably both of the anode and thecathode, the electrochemical element, which has superiorcharging/discharging characteristics capable, even when the loadrequirements change sharply and largely, of responding theretosatisfactorily, can be structured easily and reliably.

Here, in this invention, the wording “electrochemical element” means anelement, which has at least a first electrode (anode) and a secondelectrode (cathode) opposing to each other, and which has a structuresuch that, at least an electrolyte layer having the ion conductivity isprovided disposed between these first electrode and the secondelectrode. Also, the wording “electrolyte layer having the ionconductivity” means the followings; i.e., (i) a porous separator formedof insulative material, in which an electrolyte solution (or gelelectrolyte obtained by adding a gelatinizing agent to an electrolytesolution) is impregnated; (ii) a solid electrolyte film (a filmconsisting of a solid polymer electrolyte, or a film comprising an ionconductive inorganic material), (iii) a layer consisting of a gelelectrolyte obtained by adding a gelatinizing agent to the electrolytesolution, and (iv) a layer consisting of an electrolyte solution.

Any case of the above structure of (i) to (iv) may have such structurethat the electrolyte to be used for each of these is comprised in thefirst electrode and second electrode.

In this description, in the structures of (i) to (iii), the laminateditem formed of the first electrode (anode), the electrolyte layer, andthe second electrode (cathode) will be occasionally referred to as“element.” Further, as for the element, in addition to the 3-layeredstructure like the above structures of (i) to (iii), a structure of5-layer or more in which the electrode and the electrolyte layer arebuilt up alternately may be employed.

In any of structures of (i) to (iv), the electrochemical element mayhave a module structure such that plural unit cells are disposed inseries or in parallel in one case.

The electrochemical element in accordance with the invention may becharacterized in that the electrolyte layer consists of a solidelectrolyte. In this case, the solid electrolyte may be characterized byconsisting of a ceramics solid electrolyte, a solid polymer electrolyte,or a gel electrolyte obtained by adding a gelatinizing agent to a liquidelectrolyte.

In this case, an electrochemical element, in which all of theconstituent elements are of solid (for example, so called “allsolid-type cell”), can be structured. Owing to this, the weight of theelectrochemical element can be reduced, and the energy density can beincreased as well as the safety level can be increased more easily.

As the electrochemical element, when a “all solid-type cell” isstructured (particularly, a all solid-type lithium ion secondary cell isstructured), the following advantages of (I) to (IV) are obtained. Thatis, (I) since the electrolyte layer does not consist of a liquidelectrolyte but of a solid electrolyte, no liquid leaks, a superior heatresistance (high temperature stability) can be obtained, and thereaction between the electrolyte component and the electrode activematerial can be satisfactorily prevented. Therefore, superior safety andreliability of the cell can be obtained. (II) Metallic lithium can beused easily as the anode (so called “metallic lithium secondary cell”can be structured), which is difficult to be used in the electrolytelayer of liquid electrolyte; thus, the energy density can be furtherincreased. (III) When a module in which plural unit cells are disposedin one case is structured, plural unit cells can be connected in series,which is impossible to be realized in the electrolyte layer of liquidelectrolyte. Owing to this, a module, which provides various outputvoltages, particularly, comparatively large output, can be structured.(IV) Compared to the case where an electrolyte layer formed of a liquidelectrolyte is provided, flexibility of adoptable configuration of thecell is increased, and the cell can be easily structured compactly.Owing to this, the cell can be easily formed in accordance with thedisposition conditions (conditions such as disposition location, size ofdisposition space and configuration of the disposition space) in theequipment such as a potable equipment in which the cell is mounted asthe power source.

Also, the electrochemical element in accordance with the invention maybe characterized in that the electrolyte layer consists of a separatorof insulative porous substance and a liquid electrolyte or solidelectrolyte impregnated in the separator. In this case also, when thesolid electrolyte is used, a ceramics solid electrolyte, a solid polymerelectrolyte or a gel electrolyte obtained by adding a gelatinizing agentto the liquid electrolyte can be used.

Further, the invention provides a producing method of a compositeparticle for electrode,

the method comprising a granulating step for forming a compositeparticle comprising an electrode active material, a conductive additiveand a binder by bringing the conductive additive and the binder capableof binding the electrode active material and the conductive additiveinto a close contact with a particle consisting of the electrode activematerial to integrate with each other, and

the granulating step comprising:

a stock solution preparing step for preparing a stock solutioncomprising the binder, the conductive additive and a solvent;

a fluidized bed forming step for forming the particle consisting of theelectrode active material into a fluidized bed by throwing the particleconsisting of the electrode active material into a fluidizing bathe; and

a spray-drying step, in which the stock solution is sprayed into thefluidized bed comprising the particle consisting of the electrode activematerial, thereby the stock solution is allowed adhering to the particleconsisting of the electrode active material and dried to remove thesolvent from the stock solution adhered to the surface of the particleconsisting of the electrode active material to bring the particleconsisting of the electrode active material and the particle consistingof the conductive additive into a close contact with each other by meansof the binder.

By carrying out the above-described granulating step, the compositeparticle for electrode in accordance with the invention, which has theabove-described structure, can be formed easily and reliably. Therefore,by using the composite particle for electrode obtained by means of thisproducing method, an electrode having superior polarizingcharacteristics can be formed easily and reliably; and further, anelectrochemical element having superior charging/dischargingcharacteristics can be formed easily and reliably.

Here, in the granulating step of the producing method of the compositeparticle for electrode in accordance with the invention, the abovewording “allow the conductive additive and the binder coming into aclose contact with the particle consisting of the electrode activematerial to integrate with each other” means a state in which particleconsisting of the conductive additive and particle consisting of thebinder are allowed coming into contact with at least a portion of thesurface of the particle consisting of the electrode active material.That is, in the surface of the particle consisting of the electrodeactive material, if a part thereof is covered by the particle consistingof the conductive additive and particle consisting of the binder, theentire thereof does not have to be covered thereby. The “binder” used inthe granulating step of the producing method of the composite particlefor electrode in accordance with the invention is an agent which iscapable of binding the electrode active material and the conductiveadditive, which are used simultaneously.

In the producing method of the composite particle for electrode inaccordance with the invention, in order to form the composite particlefor electrode having the above-described structure more easily andreliably, in the granulating step, the temperature within the fluidizingbathe is preferably controlled to a temperature of 50° C. or more butdoes not largely exceed the melting point of the binder; morepreferably, the temperature within the fluidizing bathe is controlled to50° C. or more and the melting point or less of the binder. Depending onthe type of the binder, the melting point of the binder is, for example,approximately 200° C. When the temperature within the fluidizing batheis lower than 50° C., the following tendency appears largely; i.e., thesolvent in the spray is dried insufficiently. When the temperaturewithin the fluidizing bathe largely exceeds the melting point of thebinder, the following tendency appears largely; i.e., the binder ismolten and causes a large problem for forming the particles. When thetemperature within the fluidizing bathe is at a temperature slightlylarger than the melting point of the binder, depending on theconditions, the above problem can be satisfactorily prevented fromappearing. Also, when the temperature within the fluidizing bathe islower than the melting point of the binder, the above problem does notappear.

Further, in the producing method of the composite particle for electrodein accordance with the invention, in order to form the compositeparticle for electrode having the above-described structure more easilyand reliably, in the granulating step, the airflow generated within thefluidizing bathe is preferably an airflow of air, nitrogen gas, orinactive gas. Further, in the granulating step, the humidity within thefluidizing bathe (relative humidity) is preferably 30% or less in theabove preferred temperature range.

In the producing method of the composite particle for electrode inaccordance with the invention, in the granulating step, the solventcomprised in the stock solution is preferably capable of dissolving ordispersing the binder as well as capable of dispersing the conductiveadditive. Owing to this also, the dispersion level of the binder, theconductive additive and the electrode active material in the obtainedcomposite particles for electrode can be more increased. In order tofurther increase the dispersion level of the binder, the conductiveadditive and the electrode active material in the composite particle forelectrode, it is more preferred that the solvent comprised in the stocksolution is capable of dissolving the binder as well as capable ofdispersing the conductive additive.

Further, the producing method of the composite particle for electrode inaccordance with the invention may be characterized by using a conductivepolymer as the binder. Owing to this, in the obtained composite particlefor electrode, the conductive polymer is additionally comprised. Theabove-described polymer electrode can be formed using the compositeparticle for electrode. The conductive polymer may have the ionconductivity or the electron conductivity. In the case where theconductive polymer has the ion conductivity, an extremely satisfactoryion conduction path (ion conduction network) can be established moreeasily and reliably in the active material-containing layer forelectrode. In the case where the conductive polymer has the electronconductivity, an extremely satisfactory electron conduction path(electron conduction network) can be established more easily andreliably in the active material-containing layer for electrode.

In the producing method of the composite particle for electrode inaccordance with the invention, in the granulating step, a conductivepolymer may be additionally dissolved in the stock solution. In thiscase also, in the obtained composite particle for electrode, theconductive polymer is additionally comprised. The above-describedpolymer electrode can be formed using the composite particle forelectrode. The conductive polymer may have the ion conductivity or theelectron conductivity. In the case where the conductive polymer has theion conductivity, an extremely satisfactory ion conduction path (ionconduction network) can be established more easily and reliably in theactive material-containing layer for electrode. In the case where theconductive polymer has the electron conductivity, an extremelysatisfactory electron conduction path (electron conduction network) canbe established more easily and reliably in the activematerial-containing layer for electrode.

By using the composite particle for electrode obtained by means of theabove-described producing method of the composite particle for electrodein accordance with the invention, an electrode having superiorpolarizing characteristics can be obtained easily and reliably. Further,by using the electrode for at least one of, more preferably, both of theanode and the cathode, an electrochemical element having more superiorcharging/discharging characteristics can be formed easily and reliably.

Further, the invention provides a producing method of an electrodecomprising at least a conductive active material-containing layer whichcomprises an electrode active material, and a current collector disposedin a state being in electrically contact with the activematerial-containing layer,

the method comprising:

a granulating step of forming a composite particle comprising anelectrode active material, a conductive additive and a binder bybringing the conductive additive and the binder capable of binding theelectrode active material and the conductive additive into a closecontact with the particle consisting of the electrode active material tointegrate with each other; and

a forming step of an active material-containing layer for forming theactive material-containing layer in a portion of the collector to beformed with the active material-containing layer using the compositeparticle, and

the granulating step comprising:

a stock solution preparing step for preparing a stock solutioncomprising the binder, the conductive additive and a solvent;

a fluidized bed forming step for forming the particle consisting of theelectrode active material into a fluidized bed by throwing the particleconsisting of the electrode active material into a fluidizing bathe; and

a spray-drying step, in which the stock solution is sprayed into thefluidized bed comprising the particle consisting of the electrode activematerial, thereby the stock solution is allowed adhering to the particleconsisting of the electrode active material and dried to remove thesolvent from the stock solution adhered to the surface of the particleconsisting of the electrode active material to bring the particleconsisting of the electrode active material and the particle of theconductive additive into a close contact with each other by means of thebinder.

By carrying out the above-described granulating step, the compositeparticle, which serves as the constituent material for electrode inaccordance with the invention, which has the above-described structure,can be formed easily and reliably. Therefore, by using the compositeparticle obtained by means of this producing method, the electrodehaving superior power density and polarizing characteristics can beformed easily and reliably; and further, the electrochemical elementhaving superior charging/discharging characteristics can be formedeasily and reliably.

Here, in the granulating step of the producing method of the electrodein accordance with the invention, the above wording “allow theconductive additive and the binder coming into a close contact with theparticle consisting of the electrode active material to integrate witheach other” means a state in which the particle consisting of theconductive additive and the particle consisting of the binder areallowed coming into contact with at least a portion of the surface ofthe particle consisting of the electrode active material. That is, inthe surface of the particle consisting of the electrode active material,if a part thereof is covered by the particle consisting of theconductive additive and particle consisting of the binder, the entirethereof does not have to be covered thereby. The “binder” used in thegranulating step of the producing method of the composite particle inaccordance with the invention is an agent which is capable of bindingthe electrode active material and the conductive additive, which areused simultaneously.

In the producing method of the electrode in accordance with theinvention, in order to form the composite particle having theabove-described structure more easily and reliably, in the granulatingstep, the temperature within the fluidizing bathe is preferablycontrolled to a temperature of 50° C. or more but does not largelyexceed the melting point of the binder; more preferably, the temperaturewithin the fluidizing bathe is controlled to 50° C. or more and themelting point or less of the binder. Depending on the type of thebinder, the melting point of the binder is controlled to, for example,approximately 200° C. When the temperature within the fluidizing batheis lower than 50° C., the following tendency appears largely; i.e., thesolvent in the spray is dried insufficiently. When the temperaturewithin the fluidizing bathe largely exceeds the melting point of thebinder, the following tendency appears; i.e., the binder is molten andcauses a large problem for forming the particle. When the temperaturewithin the fluidizing bathe is at a temperature slightly larger than themelting point of the binder, depending on the conditions, the aboveproblem can be satisfactorily prevented from appearing. Also, when thetemperature within the fluidizing bathe is lower than the melting pointof the binder, the above problem does not appear.

Further, in the producing method of the composite particle in accordancewith the invention, in order to form the composite particle having theabove-described structure more easily and reliably, in the granulatingstep, the airflow generated within the fluidizing bathe is preferably anairflow formed of air, nitrogen gas, or inactive gas. Further, in thegranulating step, the humidity within the fluidizing bathe (relativehumidity) is preferably 30% or less in the above preferred temperaturerange. The wording “inactive gas” means a gas belongs to the noble gas.

In the producing method of the composite particle in accordance with theinvention, in the granulating step, the solvent comprised in the stocksolution is preferably capable of dissolving or dispersing the binder aswell as capable of dispersing the conductive additive. Owing to thisalso, the dispersion level of the binder, the conductive additive andthe electrode active material in the composite particle can be moreincreased. In order to further increase the dispersion level of thebinder, the conductive additive and the electrode active material in thecomposite particle for electrode, it is more preferred that the solventcomprised in the stock solution is capable of dissolving the binder aswell as capable of dispersing the conductive additive.

In the producing method of the electrode in accordance with theinvention, in the granulating step, a conductive polymer may beadditionally dissolved in the stock solution. In this case also, in theobtained composite particle, the conductive polymer is additionallycomprised. The above-described polymer electrode can be formed using thecomposite particle. The conductive polymer may have the ion conductivityor the electron conductivity. In the case where the conductive polymerhas the ion conductivity, an extremely satisfactory ion conduction path(ion conduction network) can be established more easily and reliably inthe active material-containing layer for electrode. In the case wherethe conductive polymer has the electron conductivity, an extremelysatisfactory electron conduction path (electron conduction network) canbe established more easily and reliably in the activematerial-containing layer for electrode.

Further, the producing method of the electrode in accordance with theinvention may be characterized by using a conductive polymer as thebinder. Owing to this, in the obtained composite particle, theconductive polymer is additionally comprised. The above-describedpolymer electrode can be formed using the composite particle. Theconductive polymer may have the ion conductivity or the electronconductivity. In the case where the conductive polymer has the ionconductivity, an extremely satisfactory ion conduction path (ionconduction network) can be established more easily and reliably in theactive material-containing layer for electrode. In the case where theconductive polymer has the electron conductivity, an extremelysatisfactory electron conduction path (electron conduction network) canbe established more easily and reliably in the activematerial-containing layer for electrode.

By using the composite particle obtained by means of the above-describedproducing method of the electrode in accordance with the invention, anelectrode having superior polarizing characteristics can be obtainedeasily and reliably. Further, by using the electrode for at least oneof, more preferably, both of the anode and the cathode, theelectrochemical element having more superior charging/dischargingcharacteristics can be formed easily and reliably.

In the forming method of the electrode of the invention, the formingstep of the active material-containing layer preferably comprises: asheet forming step in which sheet is formed by carrying out a heattreatment and a pressure treatment on fine particles comprising at leastthe composite particle to obtain a sheet comprising at least thecomposite particle, and a disposing step of the activematerial-containing layer for disposing the sheet on the collector asthe active material-containing layer.

As described above, in the forming step of the activematerial-containing layer, by forming the active material-containinglayer using the composite particle by means of the dry method, theelectrode, in which the internal resistance is satisfactorily reduced,and which has superior electrode characteristics capable of easily andsatisfactorily increasing the power density of the electrochemicalelement, can be obtained more reliably. Particularly, in this case, anelectrode of which thickness of the active material-containing layer isrelatively thick and has a large output (for example, an electrode inwhich thickness of the active material-containing layer is 80 to 120 μmor less), which has been difficult to form by means of not only theconventional dry method, needles to say, but also wet processing, can beeasily produced.

Here, the “fine particles comprising at least the composite particle”may consist of the composite particle only. Also, in the “fine particlescomprising at least the composite particle”, the binder and/or theconductive additive may further comprised. When constituents other thanthe composite particle are comprised in the fine particles, thepercentage of the composite particle within the fine particles ispreferably 80% by mass or more on the basis of the total mass of thefine particles.

Also, in this case, it may be characterized in that a first heatingmember is the collector. Owing to this, the process, in which theproduced active material-containing layer is brought into electricalcontact with the collector, can be eliminated; and thus, the workingefficiency may be increased.

In the producing method of the electrode in accordance with theinvention, the sheet-forming step is preferably carried out using a heatroll pressing machine. The heat roll-pressing machine has a pair of heatrolls, and has an arrangement such that, between the pair of the heatrolls, the “fine particles comprising at least the composite particle”are thrown in and heated and pressurized to form sheet. Owing to this,the sheet, which serves as the active material-containing layer can beformed easily and reliably.

As described above, in the producing method of the electrode inaccordance with the invention, in the forming step of the activematerial-containing layer, the active material-containing layer may beformed using the composite particle by means of the dry method. However,as described below, even when the active material-containing layer isformed by means of the wet processing, the above-described effect of theinvention can be obtained.

That is, the forming step of the active material-containing layer may becharacterized in that the forming step of the active material-containinglayer comprises: a coating liquid preparing step for preparing a coatingliquid for forming electrode by adding the composite particle to aliquid capable of dispersing or kneading the composite particle, a stepfor applying the coating liquid for forming an electrode to a portion ofthe collector to be formed with the active material-containing layer,and a step for solidifying the liquid film formed of the coating liquidfor forming an electrode applied to a portion of the collector to beformed with the active material-containing layer.

In this case also, the electrode, in which the internal resistance issatisfactorily reduced and has superior electrode characteristicscapable of easily and satisfactorily increasing the power density of theelectrochemical element, can be obtained easily and reliably. Here, asfor the “liquid capable of dispersing the composite particle,” a liquid,which does not dissolve the binder in the composite particle, ispreferred. However, within a range that, in the process to form theactive material-containing layer, the electrical contact among thecomposite particles is satisfactorily ensured, and the effect of theinvention is obtained, such a liquid, which has such a characteristic todissolve a part of the binder adjacent to the surface of the compositeparticle, may be used. Within a range that the effect of the inventionis obtained, in the liquid capable of dispersing the composite particle,the binder and the conductive additive may be further added as anothercomponent of the composite particle. In this case, the binder added asanother component is a binder, which is capable of being dissolved inthe “liquid capable of dispersing the composite particle.”

Further, when a liquid, which is capable of being kneaded with thecomposite particle, is used, the forming step of the activematerial-containing layer may be characterized by comprising a kneadedproduct preparing step of preparing a kneaded product for formingelectrode comprising the composite particle by adding the compositeparticle to the liquid, a step of applying the kneaded product forforming electrode to a portion to be formed with the activematerial-containing layer of the collector, and a step of solidifyingthe coating of the kneaded product for forming electrode applied to theportion to be formed with active material-containing layer of thecollector.

In this case also, the electrode, in which the internal resistance issatisfactorily reduced and has superior electrode characteristicscapable of easily and satisfactorily increasing the power density of theelectrochemical element, can be obtained easily and reliably.

In the producing method of the electrode in accordance with theinvention also, in order to increase the output of the electrochemicalelement more reliably by forming the active material-containing layer ofthe obtained electrode to be relatively thin, in the producing method ofan electrode, thickness T of the active material-containing layer andaverage particle diameter d of the composite particles comprised in theactive material-containing layer preferably satisfy the conditionsexpressed by following formulas (1) to (3):0.0005≦(T/d)≦1  (1)1 μm≦T≦150 μm  (2)1 μm≦d≦2000 μm  (3).

Further, the invention provides a producing method of an electrochemicalelement provided with at least an anode, a cathode and an electrolytelayer having the ion conductivity, and having a structure such that theanode and the cathode are disposed opposite to each other beinginterposed by the electrolyte layer, wherein as the electrode for one orboth of the anode and the cathode, an electrode, which is produced inaccordance with the producing method of the electrode, is used.

By using the electrode obtained by means of the above-describedproducing method of the electrode in accordance with the invention to atleast one of, preferably both of the anode and the cathode, even whenthe load requirements change sharply and largely, an electrochemicalelement, which has superior charging/discharging characteristics capableof satisfactorily responding thereto, can be obtained easily andreliably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional diagram showing a basic structure of apreferred embodiment (lithium ion secondary cell) of an electrochemicalelement in accordance with the invention.

FIG. 2 is a schematic sectional diagram showing an example of a basicstructure of a composite particle in accordance with the invention.

FIG. 3 is an illustration showing an example of granulating step whenforming an electrode.

FIG. 4 is an illustration showing an example of a sheet-forming stepwhen forming an electrode by means of the drying method.

FIG. 5 is an illustration showing an example of coating liquid preparingstep when forming an electrode by means of the wet processing.

FIG. 6 is a schematic sectional diagram showing the internal structurein an active material-containing layer for electrode in accordance withthe invention.

FIG. 7 is a schematic sectional diagram showing a basic structure ofanother embodiment of the electrochemical element in accordance with theinvention.

FIG. 8 is a schematic sectional diagram showing a basic structure ofstill another embodiment of an electrochemical element in accordancewith the invention.

FIG. 9 is an illustration showing a measuring method of internalresistance (impedance) of a composite particle for electrode in example1.

FIG. 10 is an SEM photograph showing a section of an activematerial-containing layer for electrode (electric double layeredcapacitor), which is formed in accordance with the forming method (drymethod) of the invention.

FIG. 11 is a TEM photograph showing a section (a portion identical tothe portion shown in FIG. 9) of an active material-containing layer forelectrode (electric double layered capacitor) formed in accordance withthe forming method (dry method) of the invention.

FIG. 12 is an SEM photograph showing a section of an activematerial-containing layer for electrode (electric double layeredcapacitor), which is formed in accordance with the forming method (drymethod) of the invention.

FIG. 13 is a TEM photograph showing a section (a portion identical tothe portion shown in FIG. 11) of an active material-containing layer forelectrode (electric double layered capacitor) formed in accordance withthe forming method (dry method) of the invention.

FIG. 14 is an SEM photograph showing a section of an activematerial-containing layer for electrode (electric double layeredcapacitor), which is formed in accordance with the forming method (drymethod) of the invention.

FIG. 15 is a TEM photograph showing a section (a portion identical tothe portion shown in FIG. 13) of an active material-containing layer forelectrode (electric double layered capacitor) formed in accordance withthe forming method (dry method) of the invention.

FIG. 16 is an SEM photograph showing a section of an activematerial-containing layer for electrode (electric double layeredcapacitor), which is formed by a conventional forming method (wetmethod).

FIG. 17 is a TEM photograph showing a section (a portion identical tothe portion shown in FIG. 15) of an active material-containing layer forelectrode (electric double layered capacitor) formed by a conventionalforming method (wet method).

FIG. 18 is an SEM photograph showing a section of an activematerial-containing layer for electrode (electric double layeredcapacitor), which is formed by a conventional forming method (wetmethod).

FIG. 19 is a TEM photograph showing a section (a portion identical tothe portion shown in FIG. 18) of an active material-containing layer forelectrode (electric double layered capacitor) formed by a conventionalforming method (wet method).

FIG. 20 is an SEM photograph showing a section of an activematerial-containing layer for electrode (electric double layeredcapacitor), which is formed by a conventional forming method (wetmethod).

FIG. 21 is a TEM photograph showing a section (a portion identical tothe portion shown in FIG. 20) of an active material-containing layer forelectrode (electric double layered capacitor) formed by a conventionalforming method (wet method).

FIG. 22 is a sectional diagram schematically showing partial structureof a conventional composite particle for electrode and the internalstructure in an active material-containing layer for electrode formedusing the conventional composite particles for electrode.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the invention will be described indetail with reference to the drawings. In the following descriptions,identical or equivalent portions will be given with identical referencesymbols and redundant descriptions therefore will be omitted.

FIG. 1 is a schematic sectional diagram showing a basic structure of apreferred embodiment (lithium ion secondary cell) of an electrochemicalelement in accordance with the invention. FIG. 2 is a schematicsectional diagram showing an example of a basic structure of a compositeparticle, which is prepared in a granulating step on forming anelectrode (an anode 2 and a cathode 3 in FIG. 1). Here, the electrodeprovided to the electrochemical element in accordance with theembodiment is a preferred example of the electrode in accordance withthe invention. Also, the composite particle used as constituent materialof such electrode is a preferred example of the composite particle forelectrode in accordance with the invention.

The secondary cell 1 shown in FIG. 1 comprises, principally, an anode 2,a cathode 3 and an electrolyte layer 4 disposed between the anode 2 andthe cathode 3.

Being provided with the anode 2 and the cathode 3 comprising compositeparticles P10 shown in FIG. 2, the secondary cell 1 shown in FIG. 1 iscapable of charging and discharging satisfactorily enough to respond tothe changes even when the load requirements change sharply and, inaddition, largely.

The anode 2 of the secondary cell 1 shown in FIG. 1 is constituted of acollector 24 having a film-like (plate-like) shape and a film-likeactive material-containing layer 22 disposed between the collector 24and the electrolyte layer 4. When charging, the anode 2 is connected toan anode of an external power source (both are not shown) and functionsas the cathode. The configuration of the anode 2 is not particularlylimited; but for example, a configuration of thin film as shown in FIG.1 may be employed. As for the collector 24 of the anode 2, for example,a copper foil is employed.

Also, the film-like active material-containing layer 22 of the anode 2mainly consists of the composite particle P10 shown in FIG. 2. Further,the composite particle P10 consists of a particle P1 consisting of anelectrode active material, a particle P2 consisting of a conductiveadditive and a particle P3 consisting of a binder. The average particlediameter of the composite particle P10 is not particularly limited. Thecomposite particle P10 has a structure such that the particle P1consisting of the electrode active material and the particle P2consisting of the conductive additive are not isolated from each otherbut electrically bound with each other. Accordingly, in the film-likeactive material-containing layer 22 also, a structure, in which theparticle P1 consisting of the electrode active material and the particleP2 consisting of the conductive additive are not isolated from eachother but electrically bound with each other, is formed.

The electrode active material constituting the composite particle P10comprised in the anode 2 is not particularly limited, but publicly knownelectrode active materials may be used. For example, carbon materialssuch as graphite, hardly graphitizable carbon, easily graphitizablecarbon and low temperature-calcined carbon, which are capable of storingand releasing lithium ion (intercalate, or doping and dedoping), metalssuch as Al, Si and Sn, which can form a compound with lithium, amorphouscompounds, which mainly consist of an oxide such as SiO₂ or SnO₂, andlithium titanate (Li₃Ti₅O₁₂) and the like can be mentioned.

The conductive additive constituting the composite particle P10comprised in the anode 2 is not particularly limited, but publicly knownconductive additives may be used. For example, carbon materials such ascarbon blacks, highly crystalline artificial graphite and naturalgraphite, fine powders of metal such as copper, nickel, stainless steeland iron, mixtures of the above carbon material and metal fine powder,and conductive oxides such as ITO can be mentioned.

If it is capable of binding the above particles of the electrode activematerial and the particle P2 consisting of the conductive additive, thebinder constituting the composite particle P10 comprised in the anode 2is not particularly limited. For example, fluorocarbon resins such aspolyvinyliden fluoride (PVDF), polytetrafluoroethylene (PTFE),tetrafluoroethylene-hexafluoropropylene copolymer (FEP),tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA),ethylene-tetrafluoroethylene copolymer (ETFE),polychlorotrifluoroethylene (PCTFE),ethylene-chlorotrifluoroethylene-copolymer (ECTFE), polyvinyl fluoride(PVF) can be mentioned. The binder contributes not only to binding theabove particle P1 consisting of electrode active material and theparticle P2 consisting of the conductive additive but also to bindingthe foil (collector 24) and the composite particle P10.

Further, in addition to the above, for the binder, for example,vinyliden fluoride-based fluorocarbon rubber such as vinylidenfluoride-hexafluoropropylene-based fluorocarbon rubber (VDF-HFP-basedfluorocarbon rubber), vinylidenfluoride-hexafluoropropylene-tetrafluoroethylene-based fluorocarbonrubber (VDF-HFP-TFE-based fluorocarbon rubber), vinylidenfluoride-pentafluoropropylene-based fluorocarbon rubber (VDF-PFP-basedfluorocarbon rubber), vinylidenfluoride-pentafluoropropylene-tetrafluoroethylene-based fluorocarbonrubber (VDF-PFP-TFE-based fluorocarbon rubber), vinylidenfluoride-perfluoromethylvinylether-tetrafluoroethylene-basedfluorocarbon rubber (VDF-PFMVE-TFE-based fluorocarbon rubber), vinylidenfluoride-chlorotrifluoroethylene-based fluorocarbon rubber(VDF-CTFE-based fluorocarbon rubber) may be used.

Further, in addition to the above, as for the binder, for example,polyethylene, polypropylene, polyethylene terephthalate, aromaticpolyamide, cellulose, styrene-butadiene rubber, isoprene rubber,butadiene rubber, ethylene-propylene rubber and the like are may beused. Also, thermoplastic elastomeric polymer such asstyrene-butadiene-styrene block copolymer and hydrogenated productthereof, styrene-ethylene-butadiene-styrene copolymer,styrene-isoprene-styrene block copolymer and hydrogenated productthereof may be used. Furthermore, syndiotactic 1,2-polybutadiene,ethylene-vinyl acetate copolymer, propylene-α-olefin (carbon number 2 to12) copolymer and the like may be used. Still further, a conductivepolymer may also be used.

Further, to the composite particle P10, particles consisting of aconductive polymer may be additionally added as the constituent of thecomposite particle P10. Further, when the electrode is formed by meansof the drying method using the composite particle P10, it may be addedto fine particles, which comprise at least the composite particle, asthe constituent thereof. Also, in the case where the electrode is formedby means of the wet processing using the composite particle P10, whenpreparing a coating liquid or kneaded product comprising the compositeparticle P10, a particle consisting of a conductive polymer may be addedas the constituent material of the coating liquid or kneaded product.

For example, if the conductivity based on the lithium ion is ensured,the conductive polymer is not particularly limited. For example,combined products of a monomer to be a polymer compound (polyether-basedpolymer compounds such as polyethylene oxide and polypropylene oxide,crosslinked polymer of polyether compound, polyepichlorohydrin,polyphosphazene, polysiloxane, polyvinylpyrrolidone, polyvinylidencarbonate, polyacrylonitrile, or the like) and lithium salts orlithium-based alkali metal salts such as LiClO₄, LiBF₄, LiPF₆, LiAsF₆,LiCl, LiBr, Li(CF₃SO₂)₂N and LiN(C₂F₅SO₂)₂, and the like can bementioned. As for a polymerization initiator used for combining, forexample, a photopolymerization initiator or thermal polymerizationinitiator, which is suitable for the above monomer, can be mentioned.

In order to form the secondary cell 1 into a metallic lithium secondarycell, the anode (not shown) thereof may be an electrode of metalliclithium or lithium alloy only, which also serves as the collector. Thelithium alloy is not particularly limited, but for example, an alloy ofLi—Al, LiSi, LiSn or the like (herein, LiSi is handled as an alloy) isavailable. In this case, the cathode is formed using composite particleP10, which has the constitution as described below.

The cathode 3 of the secondary cell 1 shown in FIG. 1 is constituted ofa film-like collector 34 and a film-like active material-containinglayer 32 disposed between the collector 34 and the electrolyte layer 4.When charging, the cathode 3 is connected to a cathode of an externalpower source (both are not shown) and functions as the anode. Also, theconfiguration of the cathode 3 is not particularly limited. For example,as shown in FIG. 1, the configuration may be a thin film. As for thecollector 34 of the cathode 3, for example, aluminum foil may be used.

The electrode active material constituting the composite particle P10comprised in the cathode 3 is not particularly limited. A publicly knownelectrode active material may be used. For example, lithium cobaltate(LiCoO₂), lithium nickelate (LiNiO₂), lithium manganese spinel(LiMn₂O₄), and composite metal oxide expressed by general formula:LiNi_(x)Mn_(y)Co_(z)O₂ (x+y+z=1), lithium vanadium compound, V₂O₅,olivine form LiMPO₄ (M indicates Co, Ni, Mn or Fe), lithium titanate((Li₃Ti₅O₁₂) and the like can be mentioned.

Further, as for the constituent elements other than the electrode activematerial constituting composite particle P10 comprised in the cathode 3,the same substances as those constituting the composite particle P10comprised in the anode 2 may be used. The binder constituting thecomposite particle P10 comprised in the cathode 3 also contributes notonly to binding the particle P1 consisting of the above-describedelectrode active material and the particle P2 consisting of theconductive additive, but also to bind the foil (collector 34) and thecomposite particle P10. As described above, the composite particle P10has a structure such that the particle P1 consisting of the electrodeactive material and the particle P2 consisting of the conductiveadditive are not isolated from each other but electrically bound to eachother. Therefore, in the active material-containing layer 32 also, astructure is formed in which the particle P1 consisting of the electrodeactive material and the particle P2 consisting of the conductiveadditive are not isolated from each other but electrically bound to eachother.

Here, in order to form the contact boundary among the conductiveadditive, the electrode active material and the solid polymerelectrolyte in a satisfactory size in three-dimensions, BET superficialarea of the particle P1 consisting of the electrode active materialscomprised in the above-described anode 2 and the cathode 3 is, in thecase of the cathode 3, preferably 0.1 to 1.0 m²/g, more preferably 0.1to 0.6 m²/g. And for the anode 2, the value is preferably 0.1 to 10m²/g, and more preferably 0.1 to 5 m²/g. In the case of a double-layeredcapacitor, for both of the cathode 3 and anode 2, the value ispreferably 500 to 3000 m²/g.

Further, from the same viewpoint, in the case of the cathode 3, theaverage particle diameter of the particles P1 consisting of theelectrode active material is preferably 5 to 20 μm, more preferably 5 to15 μm. In the case of the anode 2, the value is preferably 1 to 50 μm,more preferably 1 to 30 μm. Further, from the same viewpoint, the amountof the conductive additive and binder adhered to the electrode activematerial is, when expressed using a value of 100×(mass of conductiveadditive+mass of binder)/(mass of electrode active material), preferably1 to 30% by mass, more preferably 3 to 15% by mass.

The electrolyte layer 4 may be a layer formed of electrolyte, or may bea layer formed of solid electrolyte (ceramics solid electrolyte, solidpolymer electrolyte), or may be a layer formed of a separator and aliquid electrolyte impregnated in the separator and/or a solidelectrolyte.

The liquid electrolyte is prepared by dissolving an electrolytecomprising lithium in a nonaqueous solvent. The electrolyte comprisinglithium may be appropriately selected from, for example; LiClO₄, LiBF₄,LiPF₆ and the like; or lithium imide salts such as Li(CF₃SO₂)₂N,Li(C₂F₅SO₂)₂N, and LiB(C₂O₄)₂ or the like may also be used. Thenonaqueous solvent may be selected from, for example, organic solventssuch as ethers, ketones and carbonates, which are exemplified inJapanese Patent Application Laid-Open No. Show 63-121260 and the like.In the invention, particularly, carbonates are preferably used. Amongthe carbonates, particularly, a mixed solvent comprising ethylenecarbonate as the main component and added with one or more othersolvents is preferably used. The mixing ratio is, ordinarily, preferablyethylene carbonate: another solvent=5 to 70:95 to 30 (volume ratio).Since ethylene carbonate has a high freezing point as 36.4° C., and issolidified at room temperature, it cannot be used as the electrolyte fora cell by itself. However, by adding one or more other solvents having alow freezing point, the freezing point of the mixed solvent is reducedto make ethylene carbonate usable. As for the other solvents, anysolvents that lower the freezing point of ethylene carbonate may beused. For example, diethlcarbonate, dimethyl carbonate, propylenecarbonate, 1,2-dimethoxyethane, methyl ethyl carbonate, γ-butyrolactone,γ-valerolactone γ-octanoic lactone, 1,2-diethoxyethane,1,2-ethoxymethoxyethane, 1,2-dibutoxyethane, 1,3-dioxolan,tetrahydrofuran, 2-methyl-tetrahydrofuran, 4,4-dimethyl-1,3-dioxane,butylene carbonate, methyl formate and the like can be mentioned. Byusing a carbonaceous material as the active material for anode and theabove mixed solvent, the cell capacity is largely increased, and theirreversible capacity ratio can be satisfactorily lowered.

As for the solid polymer electrolyte, for example, a conductive polymerhaving ion conductivity is available.

If the conductivity of the lithium ion is ensured, the conductivepolymer is not particularly limited. For example, combined products of amonomer to be a polymer compound (polyether-based polymer compounds suchas polyethylene oxide and polypropylene oxide, crosslinked polymer ofpolyether compound, polyepichlorohydrin, polyphosphazene, polysiloxane,polyvinylpyrrolidone, polyvinyliden carbonate, polyacrylonitrile, or thelike) and lithium salts or lithium-based alkali metal salts such asLiClO₄, LiBF₄, LiPF₆, LiAsF₆, LiCl, LiBr, Li(CF₃SO₂)₂N andLiN(C₂F₅SO₂)₂, and the like can be mentioned. As for a polymerizationinitiator used for combining, for example, a photopolymerizationinitiator or thermal polymerization initiator, which is suitable for theabove monomer, can be mentioned.

Further, as for a supporting salt constituting the polymer solidelectrolyte, for example, salts such as LiClO₄, LiPF₆, LiBF₄, LiAsF₆,LiCF₃SO₃, LiCF₃CF₂SO₃, LiC(CF₃SO₂)₃, LiN(CF₃SO₂)₂, LiN(CF₃CF₂SO₂)₂,LiN(CF₃SO₂)(C₄F₉SO₂) and LiN(CF₃CF₂CO)₂, and mixtures thereof areavailable.

When a separator is used in the electrolyte layer 4, as for theconstituent material, for example, one or two or more kinds ofpolyolefins such as polyethylene and polypropylene (when two kinds ormore, a laminated product of two or more films is available), polyesterssuch as polyethylene terephthalate, thermoplastic fluorocarbon resinssuch as ethylene-tetrafluoroethylene copolymer, and celluloses areavailable. As for the configuration of the sheet, a film of microporousmembrane with the air permeability measured in accordance with themethod prescribed in JIS-P8117 of 5 to 2000 sec/100 cc or so, thicknessof 5 to 100 μm or so, a woven textile and a nonwoven cloth areavailable. A monomer of a solid electrolyte may be used after beingimpregnated in the separator and hardened to form polymer. Also, theabove-described liquid electrolyte may be used after being impregnatedinto a porous separator.

Next, a preferred embodiment of the producing method of the electrode inaccordance with the invention will be described. In the producing methodof the electrode described below, a preferred example of the producingmethod of the composite particle for electrode in accordance with theinvention is comprised.

First of all, the producing method of the composite particle P10 will bedescribed. The composite particle P10 is prepared through a granulatingstep in which the particle P1 consisting of the electrode activematerial is brought into close contact with the conductive additive andthe binder to integrate with each other to form the composite particlecomprising the electrode active material, the conductive additive andthe binder.

The above-described granulating step will be described more particularlyreferring to FIG. 3. FIG. 3 is an illustration showing an example of thegranulating step when producing the composite particle.

The granulating step comprises the following steps; i.e., a stocksolution preparing step, in which a stock solution comprising thebinder, the conductive additive and a solvent is prepared, a fluidizedbed forming step, in which an airflow is generated in a fluidizing batheand the particle consisting of an electrode active material is throwninto the airflow to form a fluidized bed with the particle consisting ofthe electrode active material, and a spray-drying step, in which thestock solution is sprayed into the fluidized bed comprising the particleconsisting of the electrode active material to allow the stock solutionadhering to the particle consisting of the electrode active material todry and remove the solvent from the stock solution adhered to thesurface of the particle consisting of the electrode active material, andbring the particle consisting of the electrode active material and theparticle consisting of the conductive additive into a close contact bymeans of the binder.

First of all, in the stock solution preparing step, using a solventcapable of dissolving the binder, the binder is dissolved in thesolvent. Then, the conductive additive is dispersed in the obtainedsolution to obtain the stock solution. In this stock solution preparingstep, a solvent (dispersion medium) capable of dispersing the binder maybe used.

Then, in the fluidized bed forming step, an airflow is generated withinthe fluidizing bathe 5 as shown in FIG. 3, and the particle P1consisting of the electrode active material is thrown into the airflow;thereby the fluidized bed is formed with the particle consisting of theelectrode active material.

Then, in the spray-drying step, as shown in FIG. 3, the drop of rawmaterial 6 is sprayed within the fluidizing bathe 5; thereby the drop ofraw material 6 is allowed adhering to the particle P1 consisting of theelectrode active material having been fluidized. At the same time, theparticle is dried within the fluidizing bathe 5 to remove the solventfrom the drop of raw material 6 adhered on the surface of the particleP1 consisting of the electrode active material, and bring the particleP1 consisting of the electrode active material and the particle P2consisting of the conductive additive into close contact with each otherby means of the binder; thus, the composite particle P10 is obtained.

In particular, the fluidizing bathe 5 is a container having, forexample, a cylindrical shape. In the bottom portion of the bathe, anopening 52 is formed for introducing warm air (or hot air) L5 from theoutside to cause the particles consisting of the electrode activematerial to convect within the fluidizing bathe 5. Also, in the sideface of the fluidizing bathe 5, an opening 54 is formed for introducingthe drop of raw material 6 to be sprayed to the particles consisting ofthe electrode active material P1 being convected within the fluidizingbathe 5. The drop of raw material 6 comprising the binder, theconductive additive and the solvent is sprayed to the particle P1consisting of the electrode active material being convected within thefluidizing bathe 5.

Here, the temperature of the ambient atmosphere where the particlesconsisting of the electrode active material P1 are placed is maintainedto a prescribed temperature at which the solvent in the drop of rawmaterial 6 can be removed swiftly (preferably, to a temperature range of50° C. to a degree not largely exceeding the melting point of thebinder, more preferably, to a temperature range from 50° C. to themelting point or less of the binder (for example, 200° C.)) bycontrolling, for example, the temperature of the warm air (or hot air),or the like. Thus, the liquid film of the stock solution, which isformed on the surface of the particle P1 consisting of the electrodeactive material, is dried substantially at the same time when the dropof raw material 6 is sprayed. Owing to this, the binder and theconductive additive are brought into a close contact with the surface ofthe particle consisting of the electrode active material; thus thecomposite particle P10 is obtained.

The solvent capable of dissolving the binder is not particularly limitedif it can dissolve the binder and disperse the conductive additive. Forexample, N-methyl-2-pyrrolidone, N,N-dimethylformamide and the like areavailable.

Next, a preferred example of the forming method of the electrode usingthe composite particle P10 will be described.

(Dry Method)

First of all, a case will be described where an electrode is formed,using the composite particle P10 produced through the above-describedgranulating step, by means of the drying method in which no solvent isused.

In this case, the active material-containing layer is formed through thefollowing forming step of the active material-containing layer. Theforming step of the active material-containing layer comprises a sheetforming step in which fine particles P12 comprising at least thecomposite particle P10 is subjected to a heat treatment and a pressuretreatment to form sheet to obtain sheet 18, which comprises at least thecomposite particle, and a disposing step of the activematerial-containing layer in which the sheet 18 is disposed on thecollector as the active material-containing layer (activematerial-containing layer 22 or active material-containing layer 32).

The dry method is a method to form an electrode without using a solvent,which has the following advantages; i.e., 1) since no solvent isrequired, the dry method is safe; 2) since the particles only areextended being applied with pressure without using a solvent, theelectrode (porous layer) can be easily built up in a high density; and3) since no solvent is used, in the drying process of the liquid filmformed of the coating liquid for forming an electrode having beenapplied on the collector, there occurs no agglomeration or unevendistribution of the particle P1 consisting of the electrode activematerial, particle P2 consisting of the conductive additive forimparting the conductivity and the particle P3 consisting of the binder,which are the problem in the wet processing method; and the like.

The sheet-forming step can be appropriately carried out using a heatroll pressing machine shown in FIG. 4.

FIG. 4 is an illustration showing an example of the sheet-forming stepwhen forming the electrode by means of the drying method (when a heatroll pressing machine is used).

In this case, as shown in FIG. 4, between a pair of heat rolls 84 and 85of a heat roll pressing machine (not shown), fine particles P12, whichcomprise at least the composite particle P10, are thrown in, and mixedand kneaded, and extended by being applying with heat and pressure toform the sheet 18. Here, the surface temperature of the heat rolls 84and 85 is preferably 60 to 120° C., and the pressure is preferably 20 to5000 kgf/cm.

Here, to the fine particles P12 comprising at least the compositeparticle P10, at least one kind of particles of the particle P1consisting of the electrode active material, particle P2 consisting ofthe conductive additive for imparting the conductivity and the particleP3 consisting of the binder may be further mixed.

Also, before throwing into the heat roll pressing machine (not shown),fine particles P12 comprising at least the composite particle P10 may bepreviously kneaded using a mixing device such as a mill.

The collector and the active material-containing layer may be broughtinto electrical contact with each other after the activematerial-containing layer is formed by the heat roll-pressing machine.However, it may be arranged so that the collector and the constituentmaterial for the active material-containing layer having been spreadover one surface of the collector are supplied to the heat rolls 84 and85; thus, the sheet of the active material-containing layer may beformed, and the electrical connection between the activematerial-containing layer and the collector may be establishedsimultaneously.

Also, to reliably obtain a high power output of the electrochemicalelement by forming the active material-containing layer of the obtainedelectrode to be comparatively thin, it is preferred to form the activematerial-containing layer in the forming step of the activematerial-containing layer, so that, thickness T of the activematerial-containing layer and average particle diameter d of thecomposite particles comprised in the active material-containing layersatisfy the conditions expressed by the following formulas (1) to (3).In particular, in the sheet forming step in the forming step of theactive material-containing layer, 1) by controlling the amount of thefine particles P12 comprising at least the composite particle P10 to bespread over the surfaces of the heat rolls 84 and 85; 2) by controllingthe gap between the heat rolls 84 and 85, or 3) by controlling thepressure when the heat rolls 84 and 85 press fine particles P12, theconditions expressed by the following formulas (1) to (3) can besatisfied:0.0005≦(T/d)≦1  (1)1 μm≦T≦150 μm  (2)1 μm≦d≦2000 μm  (3).

(Wet Processing)

Next, a preferred example will be described, in which a coating liquidfor forming an electrode is prepared using the composite particle P10produced through the above-described granulating step and an electrodeis formed using the same. First of all, an example for preparing thecoating liquid for forming an electrode will be described.

The coating liquid for forming an electrode can be obtained in thefollowing manner. That is, a mixture is prepared, in which the compositeparticle P10 produced through the granulating step, a liquid capable ofdispersing or dissolving the composite particle P10 and a conductivepolymer to be added on the basis of necessity are mixed; and a part ofthe liquid is removed from the mixed liquid to control to an appropriateviscosity for application.

In particular, when a conductive polymer is used, as shown in FIG. 5,for example, in the container 8 having a prescribed stirring device (notshown) such as a stirrer or the like, by mixing a liquid capable ofdispersing or dissolving the composite particle P10 and the conductivepolymer or a monomer, which is the constituent material for theconductive polymer, the mixture is prepared. Then, the compositeparticle P10 is added to the mixture and stirred satisfactorily; thus,the coating liquid for forming an electrode 7 is prepared.

Next, a preferred embodiment of the producing method of the electrode inaccordance with the invention using the coating liquid for forming anelectrode will be described. First of all, the coating liquid forforming an electrode is applied on the surface of the collector to forma liquid film of the coating liquid on the surface. Then, the liquidfilm is dried to form the active material-containing layer on thecollector; thus, formation of the electrode is completed. The techniqueto apply the coating liquid for forming an electrode to the surface ofthe collector is not particularly limited, but should be appropriatelydetermined corresponding to the material, configuration or the like ofthe collector. For example, such methods as metal mask printing,electrostatic coating, dip coating, spray coating, roll coating, doctorblade coating, gravure coating and screen-printing are available.

Also, to reliably obtain a high power output of the electrochemicalelement by forming the active material-containing layer of the obtainedelectrode to be comparatively thin, it is preferred to form the activematerial-containing layer in the forming step of the activematerial-containing layer, so that, thickness T of the activematerial-containing layer and average particle diameter d of thecomposite particles comprised in the active material-containing layersatisfy the conditions expressed by the following formulas (1) to (3).In particular, when the liquid film of the coating liquid for forming anelectrode is formed on the surface of the collector, the applicationamount of the coating liquid for forming an electrode is controlled.0.0005≦(T/d)≦1  (1)1 μm≦T≦150 μm  (2)1 μm≦d≦2000 μm  (3).

As for the technique to form the active material-containing layer fromthe liquid film of the coating liquid for forming an electrode, inaddition to the drying method, a technique such that, when formingactive material-containing layer from the liquid film of the coatingliquid, hardening reaction among the constituents in the liquid film(for example, polymerization reaction of a monomer to be the constituentmaterial of a conductive polymer) may be accompanied. For example, whena coating liquid for forming an electrode, which comprises a monomer tobecome a constituent material of a UV hardening resin (conductivepolymer), is used, first of all, the coating liquid for forming anelectrode is applied on the collector in the above-described prescribedmethod. Then, ultraviolet ray is irradiated to the liquid film of thecoating liquid; thereby, the active material-containing layer is formed.

In this case, compared to the case where the conductive polymer(particles consisting of conductive polymer) is previously comprised inthe coating liquid for forming an electrode, by generating conductivepolymer after forming the liquid film of the coating liquid for formingan electrode on the collector and allowing the monomer polymerizing inthe liquid film, while satisfactory state of dispersion of the compositeparticle P10 in the liquid film is substantially maintained, theconductive polymer can be generated in the spaces among the compositeparticles P10. Therefore, the state of dispersion of the compositeparticle P10 and the conductive polymer in the obtained activematerial-containing layer can be formed more satisfactorily.

That is, an ion conduction network and electron conduction network, inwhich further fine and dense particles (particles consisting of thecomposite particle P10 and the conductive polymer) are integrated witheach other, can be established in the obtained activematerial-containing layer. Therefore, in this case, a polymer electrode,which has superior polarizing characteristics capable of satisfactorilyadvancing the electrode reaction even in a range of comparatively lowoperation temperatures, can be obtained further easily and reliably.

Further, in this case, the polymerization reaction of the monomer as theconstituent material of the UV curing resin can be advanced by theultraviolet ray irradiation.

Further, on the basis of necessity, the obtained activematerial-containing layer may be subjected to an extending processing byapplying pressure using a heat plate press or heat rolls to form sheet.

In the above descriptions, as an example of forming method of theelectrode using the composite particle P10, there has been describedabout the case in which the coating liquid for forming an electrode 7comprising the composite particle P10 is prepared, and using the same,the electrode is formed. However, the forming method of the electrodeusing the composite particle P10 (wet processing) is not limited to theabove.

In the active material-containing layer (active material-containinglayer 22 or active material-containing layer 32) formed in accordancewith the above-described wet processing method or dry method, aninternal structure as schematically shown in FIG. 6 is formed. That is,in the active material-containing layer (the active material-containinglayer 22 or the active material-containing layer 32), even when theparticle P3 consisting of the binder is used, the particle P1 consistingof the electrode active material and the particle P2 consisting of theconductive additive are not isolated from each other, but such structurethat the particles thereof are electrically bound to each other isformed.

Hereinbefore, preferred embodiments of the invention have beendescribed. But the invention is not limited to the above-describedembodiments.

For example, it is necessary for the electrode in accordance with theinvention only that the active material-containing layer is formed usingthe composite particle P10 comprised in the coating liquid for formingan electrode in accordance with the invention. The structure other thanthat is not particularly limited. Also, it is necessary for anelectrochemical element only that the electrode in accordance with theinvention is provided as at least one electrode of the anode andcathode. The constitution and structure other than that is notparticularly limited. For example, in the case where the electrochemicalelement is a cell, as shown in FIG. 7, a structure of a module 100 suchthat plural unit cells (a cell comprising an anode 2, a cathode 3 and anelectrolyte layer 4, which also serves as a separator) 102 are piled upand held in a state sealed in a prescribed case 9 (packaged), may beemployed.

Further, in this case, each of the unit cells may be connected to eachother in parallel or in series. Further, for example, a cell unit suchthat plural modules 100 are electrically connected to each other inseries or in parallel may be structured. Like a cell unit 200 shown inFIG. 8, for example, a cell unit 200 of serial connection may bestructured by electrically connecting a cathode terminal 104 of onemodule 100 to an anode terminal 106 of another module 100 via a metalpiece 108.

Further, when forming the above-described module 100 and cell unit 200,the same protection circuit (not shown) or PTC (not shown) as thoseprovided to existing batteries may be additionally provided thereto.

In the above descriptions of the embodiments of the electrochemicalelement, the electrochemical element, which has a constitution ofsecondary cell, has been described. But, for example, it is sufficientthat the electrochemical element according to the invention is providedwith at least an anode, a cathode and an electrolyte layer having ionconductivity, and has such structure that the anode and the cathode aredisposed opposing to each other being interposed by the electrolytelayer. Therefore a primary cell is also applicable. As for the electrodeactive material for the composite particle P10, in addition toabove-exemplified substances, materials used for existing primary cellsmay be employed. The conductive additive and the binder may be the sameas the above-exemplified substances.

Further, the electrode according to the invention is not limited to anelectrode for cell. For example, it may be an electrode used for anelectrolytic cell, electrochemical capacitor (electric double layeredcapacitor, aluminum electrolytic capacitor etc.) or electrochemicalsensor. The electrochemical element according to the invention also isnot limited to a cell only. For example, it may be an electrolytic cell,electrochemical capacitor (electric double layered capacitor, aluminumelectrolytic capacitor etc.) or electrochemical sensor. For example, inthe case of an electrode for electric double layered capacitor, as forthe electrode active material constituting the composite particle P10, acarbon material having a high electric double layer capacitance such aspalm shell activated carbon, pitch-based activated carbon, phenol resinactivated carbon or the like may be used.

Further, as an anode used for, for instance, brine electrolysis, forexample, an electrode may be formed by using a thermally decomposedproduct of ruthenium oxide (or composite oxide of ruthenium oxide andmetal oxide other than that) as the electrode active material in theinvention to be the constituent material of the composite particle P10,and forming the active material-containing layer comprising the obtainedcomposite particle P10 on a titanium substrate.

In the case where the electrochemical element in accordance with theinvention is an electrochemical capacitor, the electrolyte solution isnot particularly limited. A nonaqueous electrolyte solution (nonaqueouselectrolyte solution using organic solvent), which is used for anelectrochemical capacitor such as a publicly known electricdouble-layered capacitor, may be used.

Further, the kind of the nonaqueous electrolyte solution 30 is notparticularly limited. However, generally, the kind is selected whiletaking into consideration the solubility and degree of disassociation ofthe solute and the viscosity of the liquid. A nonaqueous electrolytesolution having a high conductivity and high potential window (highdecomposition starting voltage) is preferred. As for the organicsolvent, propylene carbonate, diethylene carbonate and acetonitrile areavailable. As for the electrolyte, for example, quaternary ammoniumsalts such as tetraethylammonium tetrafluoroborate (borontetrafluoridetetraethylammonium) is available. In this case, contained water shouldbe strictly controlled.

EXAMPLES

Hereinafter, the invention will be described further in detail whilegiving examples and comparative examples. However, the invention is notlimited to the following examples.

Example 1

In accordance with the procedure described below, the composite particlefor electrode, which can be used for forming the activematerial-containing layer for the cathode of lithium ion secondary cell,was produced in accordance with the above-described granulating step.The composite particle P10 for electrode was formed of an electrodeactive material for the cathode (90% by mass), a conductive additive (6%by mass) and a binder (4% by mass).

As for the electrode active material for the cathode, from the compositemetal oxide expressed by a general formula:Li_(x)Mn_(y)Ni_(z)Co_(1-x-y)O_(w), particles of a composite metal oxide(BET specific surface area: 0.55 m²/g, average particle diameter: 12μm), which satisfied the conditions of x=1, y=0.33, z=0.33 and w=2, wasused. As for the conductive additive, acetylene black was used. Further,as for the binder, polyvinyliden fluoride was used.

First of all, in the stock solution preparing step, a “stock solution”(acetylene black of 3% by mass, polyvinyliden fluoride of 2% by mass)was prepared by dispersing acetylene black in the solution in whichpolyvinyliden fluoride was dissolved in N,N-dimethylformamide [(DMF):solvent].

Then, in the fluidized bed-forming step, airflow formed of the air wasgenerated within a container, which had the same structure as that ofthe fluidizing bathe 5 shown in FIG. 3, fine particles of the compositemetal oxide were thrown in to form a fluidized bed. Then, in thespray-drying step, the above-described stock solution was sprayed to thefine particles of the composite metal oxide in the state of fluidizedbed to allow the solution adhering to the surface of fine particles. Bymaintaining the temperature of the ambient atmosphere in which the fineparticles to be sprayed were placed to a fixed level, substantiallysimultaneously with the spraying, N,N-dimethylformamide was removed fromthe surface of fine particles. Thus, the acetylene black and thepolyvinyliden fluoride were brought into a close contact with thesurface of fine particles; thus, the composite particle P10 forelectrode (average particle diameter: 150 μm) was obtained.

The amount of the electrode active material, the conductive additive andthe binder used in the granulating step was controlled respectively sothat the mass ratio of these components within the finally obtainedcomposite particles P10 for electrode agreed with the above-describedvalues.

Example 2

In accordance with the procedure described below, the composite particlefor electrode, which can be used for forming the activematerial-containing layer for an anode of lithium ion secondary cell,was produced in accordance with the above-described granulating step.The composite particle P10 for electrode was constituted of an electrodeactive material for the anode (85% by mass), a conductive additive (5%by mass) and a binder (10% by mass).

As for the electrode active material for the anode, artificial graphite(BET specific surface area: 1.0 m²/g, average particle diameter: 30 μm)was used. As for the conductive additive, acetylene black was use.Further, as for the binder, polyvinyliden fluoride was used.

First of all, in the stock solution preparing step, a “stock solution”(acetylene black of 2% by mass, polyvinyliden fluoride of 4% by mass)was prepared by dispersing acetylene black in the solution in whichpolyvinyliden fluoride was dissolved in N,N-dimethylformamide [(DMF):solvent].

Then, in the spray-drying step, the above-described stock solution wassprayed to fine particles of an artificial graphite in a state offluidized bed within a container, which has the same structure as thatof the fluidizing bathe 5 shown in FIG. 3, to allow the solutionadhering to the surface of fine particles. By maintaining thetemperature of the ambient atmosphere in which the fine particles to besprayed were placed to a fixed level, substantially simultaneously withthe spraying, N,N-dimethylformamide was removed from the surface of fineparticles. Thus, the acetylene black and the polyvinyliden fluoride werebrought into a close contact with the surface of fine particles; thus,the composite particle P10 for electrode (average particle diameter: 300μm) was obtained.

The amount of the electrode active material, the conductive additive andthe binder used in the granulating step was controlled respectively sothat the mass ratio of these components within the finally obtainedcomposite particles P10 for electrode agreed with the above-describedvalues.

Example 3

In accordance with the procedure described below, the composite particlefor electrode, which can be used for forming the electrode of theelectric double layered capacitor, was produced in accordance with theabove-described granulating step. The composite particle P10 forelectrode was constituted of an electrode active material for the anode(80% by mass), a conductive additive (10% by mass) and a binder (10% bymass).

As for the electrode active material, activated carbon (BET specificsurface area: 2500 m²/g, average particle diameter: 20 μm) was used. Asfor the conductive additive, acetylene black was used. Further, as forthe binder, polyvinyliden fluoride was used.

First of all, in the stock solution preparing step, a “stock solution”(acetylene black of 2% by mass, polyvinyliden fluoride of 2% by mass)was prepared by dispersing acetylene black in the solution in whichpolyvinyliden fluoride was dissolved in N,N-dimethylformamide [(DMF):solvent].

Then, in the spray-drying step, the above-described stock solution wassprayed to the fine particles of the artificial graphite in a state offluidized bed within a container, which has the same structure as thatof the fluidizing bathe 5 shown in FIG. 3, to allow the solutionadhering to the surface of fine particles. By maintaining thetemperature of the ambient atmosphere in which the fine particles to besprayed were placed to a fixed level, substantially simultaneously withthe spraying, N,N-dimethylformamide was removed from the surface of fineparticles. Thus, the acetylene black and the polyvinyliden fluoride werebrought into a close contact with the surface of fine particles; thus,the composite particle P10 for electrode (average particle diameter: 100μm) was obtained.

The amount of the electrode active material, the conductive additive andthe binder used in the granulating step was controlled respectively sothat the mass ratio of these components within the finally obtainedcomposite particles P10 for electrode agreed with the above-describedvalues.

Comparative Example 1

An electrode was produced in accordance with the conventional electrodeproducing procedure described below. First of all, using the sameelectrode active material, conductive additive and binder as those usedin example 1, respectively, a kneaded product was obtained by mixing theabove so that mass of the electrode active material:mass of theconductive additive:mass of the binder=90:6:4.

In particular, using a planetary mill and a homogenizer, a mixture ofthe electrode active material, the conductive agent and the binder wasstirred and mixed. Then, using a heat roll apparatus, the kneadedproduct was formed into a sheet active material-containing layer, whichhad the same supporting amount of the electrode active material (50mg/cm²) and the porosity (void ratio) (25%) as those of the compositeparticle P10 for electrode in example 1, was formed on an aluminum foil(collector).

Comparative Example 2

An electrode was produced in accordance with the conventional electrodeproducing procedure described below. First of all, using the sameelectrode active material, conductive additive and binder as those usedin example 2, respectively, a kneaded product was obtained by mixing theabove so that mass of the electrode active material:mass of theconductive additive:mass of the binder=85:5:10.

In particular, using a planetary mill and a homogenizer, a mixture ofthe electrode active material, the conductive agent and the binder wasstirred and mixed. Then, using a heat roll apparatus, the kneadedproduct was formed into a sheet active material-containing layer, whichhad the same supporting amount of the electrode active material (32mg/cm²) and the porosity (void ratio) (35%) as those of the compositeparticles P10 for electrode in example 1, was formed on a copper foil(collector).

Comparative Example 3

An electrode was produced in accordance with the conventional electrodeproducing procedure described below. First of all, using the sameelectrode active material, conductive additive and binder as those usedin example 3, respectively, a kneaded product was obtained by mixing theabove so that mass of the electrode active material:mass of theconductive additive:mass of the binder=80:10:10.

In particular, using a planetary mill and a homogenizer, a mixture ofthe electrode active material, the conductive agent and the binder wasstirred and mixed. Then, using a heat roll apparatus, the kneadedproduct was formed into a sheet active material-containing layer, whichhad the same supporting amount of the electrode active material (10mg/cm²) and the porosity (void ratio) (50%) as those of the compositeparticles P10 for electrode in example 2, was formed on an aluminum foil(collector).

[Producing of Measurement Cell for Internal Resistance (Impedance)Measurement Test of Composite Particles]

In order to measure the internal resistance (impedance) of the compositeparticle P10 of example 1, a measurement cell shown in FIG. 9 wasproduced. FIG. 9 is an illustration showing the measuring method of theinternal resistance (impedance) of the composite particle for electrodein example 1.

The measurement cell 20 will be described. As shown in FIG. 9, themeasurement cell 20 was disposed in a glove box 9. The inside of theglove box 9 was filled with argon gas. As shown in FIG. 9, themeasurement cell 20 was constituted of, principally, a cathode C and ananode A opposite to each other and a layer E of electrolyte solutiondisposed between the anode A and the cathode C.

As shown in FIG. 9, the anode A was constituted of a metallic lithiumfoil A2 (film thickness: 200 μm, area of the electrode: circular ofdiameter 15 mm) and a terminal A1 of a platinum wire connected to therear surface of the metallic lithium foil A2 (the surface at the sidewhich is not brought into contact with the layer E of the electrolytesolution). Also, as shown in FIG. 9, the cathode C was constituted ofthe composite particle P10 for electrode of example 1 and a terminal C1of a platinum wire which was electrically connected to the compositeparticle P10 for electrode.

The composite particle P10 for electrode and the terminal C1 of aplatinum wire were electrically connected to each other in a state thatboth contact resistance values became the minimum. Also, the compositeparticle P10 for electrode of the cathode C was impregnated in the layerE of the electrolyte solution, and the position thereof was fixed sothat the distance between the metallic lithium foil A2 and the compositeparticle P10 for electrode was constant (1 cm).

The layer E of electrolyte solution was constituted of electrolytesolution in which LiClO₄ was dissolved in a solvent in which ethylenecarbonate and propylene carbonate were mixed at a volume ratio of 3:1 sothat the density thereof was 1 mol/L.

[Internal Resistance (Impedance) Measurement Test of CompositeParticles]

On each measurement cell, in which the composite particle P10 forelectrode of example 1 was used for the electrode, the internalresistance (impedance) was measured when the measuring temperature wasroom temperature (25° C.).

The internal resistance (impedance) was measured in a manner asdescribed below. That is, on one of the composite particle P10 (1particle) for electrode of example 1, cyclic voltammetry measurement wasperformed. Based on this, the equilibrium capacity value of thecomposite particle P10 for electrode was calculated. Then, on one of thecomposite particle P10 (1 particle) for electrode of example 1, theimpedance was measured; and from the data of the obtained compleximpedance plots, the charge transfer resistance value of the compositeparticle P10 for electrode was calculated as the impedance value. Then,by dividing the impedance value by the equilibrium capacity value, theimpedance value normalized by the equilibrium capacity value(=(theimpedance value)/(the equilibrium capacity value)) was obtained. Theresult is shown in table 1. This value is the relative value assumingthat the value of the following comparative example 1 is 1.

[Internal Resistance (Impedance) Measurement Test of the Electrode ofComparative Example 1]

On the electrode of the comparative example 1, the internal resistance(impedance) was measured when the measuring temperature was roomtemperature (25° C.).

The internal resistance (impedance) was measured in a manner asdescribed below. That is, on the active material-containing layer forelectrode of comparative example 1, cyclic voltammetry measurement wasperformed. Based on this, the equilibrium capacity value of the activematerial-containing layer was calculated. Then, on activematerial-containing layer, the impedance was measured, and from the dataof the obtained complex impedance plots, the charge transfer resistancevalue of the active material-containing layer was calculated as theimpedance value. Then, by dividing the impedance value by theequilibrium capacity value, the impedance value normalized by theequilibrium capacity value (=(the impedance value)/(the equilibriumcapacity value)) was obtained. The result is shown in table 1. Assumingthat this value is 1, other examples were compared.

[Internal Resistance (Impedance) Measurement Test of Electrode ActiveMaterial Comprised in Composite Particle for Electrode of Example 1]

On particles of electrode active material comprised in the compositeparticle P10 for electrode of example 1, the internal resistance(impedance) was measured when the measurement temperature was roomtemperature (25° C.).

The measurement of the internal resistance (impedance) was carried outas described below. That is, on one particle of the particles ofelectrode active material of the composite particle P10 for electrode ofexample 1 (one particle), cyclic voltammetry measurement was performed;and based on this, the equilibrium capacity value of the particle of theelectrode active material was calculated. Then, on one particle of theelectrode active material comprised in the composite particle P10 forelectrode of example 1 (one particle), the impedance was measured; andfrom the data of the obtained complex impedance plots, the chargetransfer resistance value of the particles of electrode active materialwas calculated as the impedance value. Then, the impedance value wasdivided by the equilibrium capacity value; thus, the impedance valuenormalized based on the equilibrium capacity value (=(the impedancevalue)/(the equilibrium capacity value)) was obtained. The result ofthis is shown table 1. The values in Table 1 are dimensionless valuessince calculation was made assuming that the value of the comparativeexample 1 was 1 (reference). TABLE 1 Impedance normalized based onequilibrium capacity Example 1 (composite 0.07 particles) Active 1.00material-containing layer of the comparative example 1 Active materialparticle 0.28

As demonstrated in the result shown in Table 1, it was confirmed that,when the electrode was produced from the composite particles of examples1 to 3, compared to the internal resistance of the activematerial-containing layer for electrode produced in accordance with theconventional producing method, the internal resistance of the activematerial-containing layer was satisfactorily low.

Further, as demonstrated by the result shown in Table 1, it wasconfirmed that, even when the binder was comprised, the compositeparticles of the examples 1 to 3, the internal resistance value thereofwas lower than the internal resistance value of the used electrodeactive material itself.

Example 4

(1) Producing of Composite Particle

First of all, in accordance with the following procedure, a compositeparticle, which can be used for forming the active material-containinglayer for the cathode of a lithium ion secondary cell, was produced inaccordance with the above-described granulating step. The compositeparticle P10 was constituted of an electrode active material for thecathode (92% by mass), a conductive additive (4.8% by mass) and a binder(3.2% by mass).

As for the electrode active material for the cathode, from the compositemetal oxide expressed by a general formula:Li_(x)Mn_(y)Ni_(z)Co_(1-x-y)O_(w), particles of a composite metal oxide(BET specific surface area: 0.55 m²/g, average particle diameter: 12μm), which satisfies the conditions of x=1, y=0.33, z=0.33 and w=2, wasused. As for the conductive additive, acetylene black was used. Further,as for the binder, polyvinyliden fluoride was used.

First of all, in the stock solution preparing step, a “stock solution”(acetylene black of 3% by mass, polyvinyliden fluoride of 2% by mass)was prepared by dispersing acetylene black in the solution in whichpolyvinyliden fluoride was dissolved in N,N-dimethylformamide [(DMF):solvent].

Then, in the fluidized bed-forming step, airflow of the air wasgenerated within a container, which had the same structure as that ofthe fluidizing bathe 5 shown in FIG. 3, fine particles of a compositemetal oxide were thrown in to form a fluidized bed. Then, in thespray-drying step, the above-described stock solution was sprayed to thefine particles of the composite metal oxide in the state of fluidizedbed to allow the solution adhering to the surface of fine particles. Bymaintaining the temperature of the ambient atmosphere in which the fineparticles to be sprayed were placed to a fixed level, substantiallysimultaneously with the spraying, N,N-dimethylformamide was removed fromthe surface of fine particles. Thus, the acetylene black and thepolyvinyliden fluoride were brought into a close contact with thesurface of fine particles; thus, the composite particle P10 forelectrode (average particle diameter: 200 μm) was obtained.

The amount of the electrode active material, the conductive additive andthe binder used in the granulating step was controlled respectively sothat the mass ratio of these components within the finally obtainedcomposite particles P10 for electrode agreed with the above-describedvalues.

(2) Producing of Electrode (Cathode)

The electrode (cathode) was produced in accordance with theabove-described dry method. First of all, using a heat roll pressmachine, which has the same structure as that shown in FIG. 4, thecomposite particle P10 (average particle diameter: 200 μm) was thrownthereinto; thus, sheet (width: 10 cm), which serves as the activematerial-containing layer, was produced (sheet forming step). Here, theheating temperature was 120° C.; and the pressurizing condition was 200kgf/cm line pressure. Then, this sheet was punched out to obtain adisk-like active material-containing layer (diameter: 15 mm).

Then, a hot melt conductive layer (thickness: 5 μm) was formed on onesurface of a disk-like collector (aluminum foil, diameter: 15 mm,thickness: 20 μm). The hot melt conductive layer is a layer (acetyleneblack: 20% by mass, polyvinyliden fluoride: 80% by mass), which consistsof the same conductive additive (acetylene black) as that used forproducing the composite particle and the same binder (polyvinylidenfluoride) as that used for producing the composite particle.

Then, the previously produced sheet, which serves as the activematerial-containing layer, was disposed on the hot melt conductive layerand bonded by means of thermo compression. As for the conditions ofthermo compression bonding, thermo compression bonding time: for oneminute, heating temperature was 180° C., and the pressurizing conditionwas 30 kgf/cm². Thus, the electrode (cathode) having the activematerial-containing layer of thickness: 100 μm, active materialsupporting amount: 30 mg/cm², and void percent: 25% by volume wasobtained.

Example 5

(1) Producing of Composite Particle

First of all, in accordance with the procedure described below, acomposite particle, which can be used for forming the activematerial-containing layer for the anode of lithium ion secondary cell,was produced in accordance with the granulating step. The compositeparticle P10 was constituted of an electrode active material for theanode (88% by mass), a conductive additive (4% by mass) and a binder (8%by mass).

As for the electrode active material for the anode, a particle of anartificial graphite, which is a fibrous black lead material (BETspecific surface area: 1.0 m²/g, average particle diameter: 19 μm) wasused. As for the conductive additive, acetylene black was use. Further,as for the binder, polyvinyliden fluoride was used.

First of all, in the stock solution preparing step, a “stock solution”(acetylene black of 3% by mass, polyvinyliden fluoride of 2% by mass)was prepared by dispersing acetylene black into the solution in whichpolyvinyliden fluoride was dissolved in N,N-dimethylformamide [(DMF):solvent].

Then, in the fluidized bed-forming step, airflow of the air wasgenerated within a container, which had the same structure as that ofthe fluidizing bathe 5 shown in FIG. 3, fine particles of a compositemetal oxide were thrown in to form a fluidized bed. Then, in thespray-drying step, the above-described stock solution was sprayed to thefine particles of the composite metal oxide in the state of fluidizedbed to allow the solution adhering to the surface of fine particles. Bymaintaining the temperature of the ambient atmosphere in which the fineparticles to be sprayed were placed to a fixed level, substantiallysimultaneously with the spraying, N,N-dimethylformamide was removed fromthe surface of fine particles. Thus, the acetylene black and thepolyvinyliden fluoride were brought into a close contact with thesurface of fine particles; thus, the composite particle P10 forelectrode (average particle diameter: 200 μm) was obtained.

The amount of the electrode active material, the conductive additive andthe binder used in the granulating step was controlled respectively sothat the mass ratio of these components within the finally obtainedcomposite particle P10 for electrode agreed with the above-describedvalues.

(2) Producing of Electrode (Anode)

The electrode (anode) was produced in accordance with theabove-described dry method. First of all, using a heat roll pressmachine, which has the same structure as that shown in FIG. 4, thecomposite particle P10 (average particle diameter: 200 μm) was thrownthereinto, sheet (width: 10 cm), which serves as the activematerial-containing layer, was produced (sheet forming step). Here, theheating temperature was 120° C.; and the pressurizing condition was 200kgf/cm line pressure. Then, this sheet was punched out to obtain adisk-like active material-containing layer (diameter: 15 mm).

Then, a hot melt conductive layer (thickness: 5 μm) was formed on onesurface of a disk-like collector (copper foil, diameter: 15 mm,thickness: 20 μm). The hot melt conductive layer is a layer (acetyleneblack: 30% by mass, polyvinyliden fluoride: 70% by mass), which consistsof the same conductive additive (acetylene black) as that used forproducing the composite particle and the binder (methyl methacrylate).

Then, the sheet previously produced, which served as the activematerial-containing layer, was disposed on the hot melt conductive layerand bonded by means of thermo compression. As for the conditions ofthermo compression bonding, thermo compression bonding time: for 30seconds, heating temperature was 100° C., and the pressurizing conditionwas 10 kgf/cm². Thus, the electrode (anode) of the activematerial-containing layer, of which thickness: 100 μm, active material:15 mg/cm², and void percent: 25% by volume was obtained.

Comparative Example 4

An electrode (cathode) was produced in accordance with the followingconventional electrode forming procedure (wet processing). As for theconstituent material for the electrode, the same electrode activematerial, conductive additive and binder as those used in example 4respectively were used, and controlled so that mass of the electrodeactive material:mass of the conductive additive:mass of the binder wasthe same as those in example 4. The used collector (provided with a hotmelt layer) was also the same as that used in example 4.

First of all, the binder was dissolved in N-methyl pyrrolidone (NMP) toprepare the binder solution (binder density with reference to the totalmass of the solution: 5% by mass). Then, the electrode active materialand the conductive additive were thrown into the binder solution at theabove-described ratio and mixed by a hyper mixer to obtain the coatingliquid. Then, the coating liquid was applied on the hot melt layer ofthe collector for the cathode by a doctor blade method. Then, the liquidfilm of the coating liquid formed on the collector for the cathode wasdried.

Then, the obtained collector for the cathode in a state that the liquidfilm was dried was extended by applying pressure using a roller pressmachine. Here, the heating temperature was 180° C., heating time was forone minute, and the pressurizing condition was 30 kgf/cm². Thus, theelectrode (cathode) having the active material-containing layer withthickness: 100 μm, active material supporting amount: 30 mg/cm² and voidpercent: 25% by volume was obtained.

Comparative Example 5

An electrode (anode) was produced in accordance with the followingconventional electrode forming procedure (wet processing). As for theconstituent material for electrode, the same electrode active material,conductive additive and binder as those used in example 4 respectivelywere used, and controlled so that mass of the electrode activematerial:mass of the conductive additive:mass of the binder was the sameas those in example 5. The used collector (provided with a hot meltlayer) was also the same as that used in example 5.

First of all, the binder was dissolved in N-methyl pyrrolidone (NMP) toprepare the binder solution (binder density with reference to the totalmass of the solution: 5% by mass). Then, the electrode active materialand the conductive additive were thrown into the binder solution at theabove-described ratio and mixed by a hyper mixer to obtain the coatingliquid. Then, the coating liquid was applied on the hot melt layer ofthe collector for the anode by a doctor blade method. Then, the liquidfilm of the coating liquid formed on the collector for the anode wasdried.

Then, the obtained collector for the anode in a state that the liquidfilm was dried was extended by applying pressure using a roller pressmachine. Here, the heating temperature was 100° C., heating time was for30 seconds, and the pressurizing condition was 10 kgf/cm². Thus, theelectrode (anode) having the active material-containing layer withthickness: 100 μm, active material supporting amount: 15 mg/cm² and voidpercent: 25% by volume was obtained.

[Electrode Characteristics Assessment Test]

Electrochemical cells were produced by using each of electrodes inexamples 4 and 5 and comparative examples 4 and 5 as a “test electrode(work electrode)” and a lithium metal foil (diameter: 15 mm, thickness:100 μm) as a counter electrode, and the following assessment tests weremade to assess electrode characteristics of each electrode (testelectrode). The results of the assessment test are shown in table 2.

(1) Preparation of Electrolyte Solution

The electrolyte solution for forming the electrolyte layer was preparedin accordance with the preparing procedure. That is, LiClO₄ wasdissolved in the solvent [solvent in which ethylene carbonate (EC) anddiethyl carbonate (DEC) were mixed at volume ratio 1:1] so that volumemole concentration was 1 mol/L.

(2) Producing of Electrochemical Cell for Electrode CharacteristicsAssessment Test

First of all, the test electrode and the counter electrode were setopposing to each other, and a separator (diameter: 15 mm, thickness: 30μm) formed of polyethylene porous film was disposed therebetween to forma laminated product (element), in which the anode, the separator and thecathode were built up in this order. A lead (width: 10 mm, length: 25mm, thickness: 0.50 mm) was connected to each of the anode and thecathode of the laminated product by means of an ultrasonic welding.Then, the laminated product was placed in an airtight container, whichserved as a mold for the electrochemical cell, and the preparedelectrolyte solution was poured, and maintained in a state that aspecific pressure was applied thereto from the both sides of the anodeand cathode of the laminated product. Thus, electrochemical cell wasproduced for each test electrode.

(3) Electrode Characteristics Assessment Test

In the case where the test electrode was the cathode (the electrode inexample 4 and electrode in comparative example 4), using the redoxpotential of the lithium metal of the counter electrode as thereference, the potential of the test electrode was polarized in apotential range of +2.5 V to +4.3 V (constant current-constant voltage).The measurement assessment tests were carried out at 25° C.

In the case where the test electrode was the anode (the electrode inexample 5 and electrode in comparative example 5), using the redoxpotential of the lithium metal of the counter electrode as thereference, the potential of the test electrode was polarized in apotential range of +0.01 V to +3 V (constant current-constant voltage).The measurement assessment tests were carried out at 25° C.

From the obtained polarizing characteristics, capacity of activesubstance (A) (mAh·g⁻¹) of the respective electrodes at the point oftest and the maximum current density (mA·cm⁻²) capable of pulling outthe capacity of active substance (A) were obtained. The results areshown in Table 2. TABLE 2 Capacity of active Maximum current densitysubstance (A) at the capable of pulling out the point of test/ capacityof active substance mAh · g⁻¹ (A)/mA · cm⁻² Example 4 155 9.2 Example 5311 8.8 Comparative 155 0.4 example 4 Comparative 305 0.8 example 5

From the results shown in Table 2, the following fact was confirmed.That is, compared to the electrodes of comparative examples 4 and 5, inthe electrodes of examples 4 and 5, the maximum current density capableof pulling out the capacity of active substance (A) is larger; andaccordingly, they have superior output characteristics. Based on theabove result, it is understood that, in the active material-containinglayer for electrodes in examples 4 and 5, the electrode active materialand the conductive additive are electrically bound to each other withoutbeing isolated from each other and, therefore, satisfactory electronconduction network and ion conduction network are formed.

(Observation of Section of Active Material-Containing Layer)

Pieces of a part of the electrodes of *example 4 and *comparativeexample 4 punched out in a rectangular shape (5 mm×5 mm) were obtained.On the active material-containing layer of the respective pieces ofelectrodes *example 4 and *comparative example 4, resin-fillingtreatment (resin: epoxy) was made, and further, the surface of theobtained active material-containing layers was polished. Then, using amicrotome, from each of the pieces of the electrodes in *example 4 and*comparative example 4, measurement samples (0.1 mm×0.1 mm) forobserving by means of an SEM photograph and a TEM photograph wereobtained. On each of the measurement samples, SEM photograph and TEMphotograph were taken.

SEM photographs and TEM photographs of the active material-containinglayer for electrode in *example 4 are shown in FIGS. 10 to 15. And SEMphotographs and TEM photographs of the active material-containing layerfor electrode in *comparative example 4 are shown in FIGS. 16 to 21.

FIG. 10 is an SEM photograph showing a section of the activematerial-containing layer for electrode (electric double layeredcapacitor), which was formed in accordance with the forming method (drymethod) of the invention. FIG. 11 is a TEM photograph showing a section(a portion identical to the portion shown in FIG. 10) of the activematerial-containing layer for electrode (electric double layeredcapacitor) formed in accordance with the forming method (dry method) ofthe invention.

FIG. 12 is an SEM photograph showing a section of the activematerial-containing layer for electrode (electric double layeredcapacitor), which was formed in accordance with the forming method (drymethod) of the invention. FIG. 13 is a TEM photograph showing a section(a portion identical to the portion shown in FIG. 12) of the activematerial-containing layer for electrode (electric double layeredcapacitor) formed in accordance with the forming method (dry method) ofthe invention.

FIG. 14 is an SEM photograph showing a section of the activematerial-containing layer for electrode (electric double layeredcapacitor), which was formed in accordance with the forming method (drymethod) of the invention. FIG. 15 is a TEM photograph showing a section(a portion identical to the portion shown in FIG. 14) of the activematerial-containing layer for electrode (electric double layeredcapacitor) formed in accordance with the forming method (dry method) ofthe invention.

FIG. 16 is an SEM photograph showing a section of an activematerial-containing layer for electrode (electric double layeredcapacitor), which was formed in accordance with the conventionalproducing method (wet process). FIG. 17 is a TEM photograph showing asection (a portion identical to the portion shown in FIG. 16) of anactive material-containing layer for electrode (electric double layeredcapacitor) formed in accordance with the conventional producing method(wet process).

FIG. 18 is an SEM photograph showing a section of an activematerial-containing layer for electrode (electric double layeredcapacitor), which was formed in accordance with the conventionalproducing method (wet process). FIG. 19 is a TEM photograph showing asection (a portion identical to the portion shown in FIG. 18) of anactive material-containing layer for electrode (electric double layeredcapacitor) formed in accordance with the conventional producing method(wet process).

FIG. 20 is an SEM photograph showing a section of an activematerial-containing layer for electrode (electric double layeredcapacitor), which was formed in accordance with the conventionalproducing method (wet process). FIG. 21 is a TEM photograph showing asection (a portion identical to the portion shown in FIG. 20) of anactive material-containing layer for electrode (electric double layeredcapacitor) formed in accordance with the conventional producing method(wet process).

As demonstrated by the results shown in FIGS. 10 to 15, it was confirmedthat the electrode of *example 4 has the following structure. That is,for example, from the observation result of photographed areas of R1 toR5 in FIG. 10 and the photographed areas of R1A to R5A in FIG. 11 (thesame portions as those of R1 to R5 in FIG. 10 respectively), it wasconfirmed that neighboring activated carbon particles were electricallyand physically connected to each other by the agglomerate consisting ofthe conductive additive and the binder, and that satisfactory electronconduction network and ion conduction network were formed.

The internal structure of the above active material-containing layer wasconfirmed more clearly from the observation result of photographed areasof R6 to R8 in FIG. 12 and photographed areas of R6A to R8A in FIG. 13(the same portion of R6 to R8 in FIG. 12 respectively), and from theobservation result of photographed area of R9 in FIG. 14 andphotographed area of R9A in FIG. 15 (the same portion of R9 in FIG. 14),which are the photographs of which magnification are changed.

On the other hand, as demonstrated by the results shown in FIGS. 16 to17, it was confirmed that the electrode of *comparative example 4 hadthe following structure. That is, for example, from the observationresult of photographed areas of R10 to R50 in FIG. 16 and thephotographed areas of R10A to R50A in FIG. 17 (the same portions asthose of R10 to R50 in FIG. 16 respectively), it was clearly observedthat the agglomerate consisting of the conductive additive and thebinder existed being electrically and physically isolated from theactivated carbon particle, and compared to the activematerial-containing layer in *example 4, the electron conduction networkand the ion conduction network were not formed satisfactorily.

The internal structure of the above active material-containing layer wasconfirmed more clearly as the observation result of photographed areasof R60 to R80 in FIG. 18 and photographed areas of R60A to R80A in FIG.19 (the same portion of R60 to R80 in FIG. 18 respectively) and theobservation result of photographed area of R90 in FIG. 20 andphotographed area of R90A in FIG. 21 (the same portion of R90 in FIG.20), which are the photographs of which magnification is changed.

INDUSTRIAL APPLICABILITY

As described above, according to the invention, a composite particle forelectrode, which is capable of easily and reliably forming an electrodehaving superior electrode characteristics even when a binder is used asthe constituent material for electrode, can be obtained.

Also, according to the invention, the electrode, of which internalresistance is satisfactorily reduced, and which has superior electrodecharacteristics capable of easily and satisfactorily increasing thepower density of the electrochemical element can be provided.

Further, according to the invention, by using the above electrode, theelectrochemical element, which has superior charging/dischargingcharacteristics capable of, even when the load requirements sharply and,in addition, largely changes, satisfactorily responding thereto, can beprovided.

Further, according to the invention, the producing method, which iscapable of easily and reliably obtaining each of the above compositeparticles for electrode, electrode and electrochemical element inaccordance with the invention, can be provided.

1.-36. (canceled)
 37. A composite particle for electrode comprising anelectrode active material, a conductive additive having electronconductivity and a binder capable of binding the electrode activematerial and the conductive additive, the composite particle forelectrode being formed through a granulating step in which theconductive additive and the binder are brought into a close contact withthe particle consisting of the electrode active material and integratedwith each other, and the granulating step comprising: a stock solutionpreparing step for preparing a stock solution comprising the binder, theconductive additive and a solvent; a fluidized bed forming step forforming the particle consisting of the electrode active material into afluidized bed by throwing the particle consisting of the electrodeactive material into a fluidizing bathe; and a spray-drying step, inwhich the stock solution is sprayed into the fluidized bed comprisingthe particle consisting of the electrode active material, thereby thestock solution is allowed adhering to the particle consisting of theelectrode active material and dried to remove the solvent from the stocksolution adhered to the surface of the particle consisting of theelectrode active material to bring the particle consisting of theelectrode active material and the particle consisting of the conductiveadditive into a close contact with each other by means of the binder.38. The composite particle for electrode according to claim 37, whereinthe binder consists of a conductive polymer.
 39. The composite particlefor electrode according to claim 38, wherein the composite particle hasthe ion conductivity.
 40. The composite particle for electrode accordingto claim 38, wherein the composite particle has the electronconductivity.
 41. The composite particle for electrode according toclaim 37, wherein the composite particle further comprises a conductivepolymer.
 42. The composite particle for electrode according to claim 37,wherein the electrode active material is an active material usable forat least one of the cathode and the anode of a primary cell or asecondary cell.
 43. The composite particle for electrode according toclaim 37, wherein the electrode active material is a carbon material ora metal oxide having the electron conductivity usable for the electrodesconstituting an electrochemical capacitor.
 44. An electrode comprisingat least a conductive active material-containing layer comprising, asthe structural material, composite particles composed of an electrodeactive material, a conductive additive having electron conductivity, anda binder capable of binding the electrode active material and theconductive additive, and a current collector situated in electricalcontact with the active material-containing layer, the compositeparticle being formed through a granulating step in which the conductiveadditive and the binder are brought into a close contact with theparticle consisting of the electrode active material and integrated witheach other, and the electrode active material and the conductiveadditive being non-isolated and electrically linked with each other inthe active material-containing layer.
 45. The electrode according toclaim 44, wherein the granulating step comprises: a stock solutionpreparing step for preparing a stock solution comprising the binder, theconductive additive and a solvent; a fluidized bed forming step forforming the particle consisting of the electrode active material into afluidized bed by throwing the particle consisting of the electrodeactive material into a fluidizing bathe; and a spray-drying step, inwhich the stock solution is sprayed into the fluidized bed comprisingthe particle consisting of the electrode active material, thereby thestock solution is allowed adhering to the particle consisting of theelectrode active material and dried to remove the solvent from the stocksolution adhered to the surface of the particle consisting of theelectrode active material to bring the particle consisting of theelectrode active material and the particle consisting of the conductiveadditive into a close contact with each other by means of the binder.46. The electrode according to claim 44, wherein thickness T of theactive material-containing layer and average particle diameter d of thecomposite particle comprised in the active material-containing layersatisfy the conditions expressed by following formulas (1) to (3):0.0005≦(T/d)≦1  (1)1 μm≦T≦150 μm  (2)1 μm≦d≦2000 μm  (3).
 47. The electrode according to claim 44, whereinthe active material-containing layer further comprises a conductivepolymer.
 48. The electrode according to claim 47, wherein the conductivepolymer has the ion conductivity.
 49. The electrode according to claim44, wherein the composite particle further comprises a conductivepolymer.
 50. The electrode according to claim 44, wherein the binderconsists of a conductive polymer.
 51. An electrochemical elementcomprising at least an anode, a cathode and an electrolyte layer havingthe ion conductivity and having a structure such that the anode and thecathode are disposed opposite to each other being interposed by theelectrolyte layer, the electrode according to claim 44 being provided asthe electrode of one or both of the anode and the cathode.
 52. Aproducing method of a composite particle for electrode, the methodcomprising a granulating step for forming a composite particlecomprising an electrode active material, a conductive additive and abinder by bringing the conductive additive and the binder capable ofbinding the electrode active material and the conductive additive into aclose contact with a particle consisting of the electrode activematerial to integrate with each other, and the granulating stepcomprising: a stock solution preparing step for preparing a stocksolution comprising the binder, the conductive additive and a solvent; afluidized bed forming step for forming the particle consisting of theelectrode active material into a fluidized bed by throwing the particleconsisting of the electrode active material into a fluidizing bathe; anda spray-drying step, in which the stock solution is sprayed into thefluidized bed comprising the particle consisting of the electrode activematerial, thereby the stock solution is allowed adhering to the particleconsisting of the electrode active material and dried to remove thesolvent from the stock solution adhered to the surface of the particleconsisting of the electrode active material to bring the particleconsisting of the electrode active material and the particle consistingof the conductive additive into a close contact with each other by meansof the binder.
 53. The producing method of a composite particle forelectrode according to claim 52, wherein, in the granulating step, thetemperature within the fluidizing bathe is controlled to 50° C. or moreand melting point or less of the binder.
 54. The producing method of acomposite particle for electrode according to claim 52, wherein, in thegranulating step, the airflow generated within the fluidizing bathe isan airflow formed of air, nitrogen gas or inactive gas.
 55. Theproducing method of a composite particle for electrode according toclaim 53, wherein the solvent comprised in the stock solution is capableof dissolving or dispersing the binder as well as capable of dispersingthe conductive additive.
 56. The producing method of a compositeparticle for electrode according to claim 52, wherein a conductivepolymer is used as the binder.
 57. The producing method of a compositeparticle for electrode according to claim 53, wherein a conductivepolymer is further dissolved in the stock solution.
 58. The producingmethod of a composite particle for electrode according to claim 56,wherein the conductive polymer has the ion conductivity.
 59. Theproducing method of a composite particle for electrode according toclaim 56, wherein the conductive polymer has the electron conductivity.60. The producing method of a composite particle for electrode accordingto claim 52, wherein the electrode active material is an active materialusable for at least one of the cathode and the anode of a primary cellor a secondary cell.
 61. The producing method of a composite particlefor electrode according to claim 52, wherein the electrode activematerial is a carbon material or a metal oxide having electronconductivity usable for an electrode constituting an electrochemicalcapacitor.
 62. A producing method of an electrode comprising at least aconductive active material-containing layer which comprises an electrodeactive material, and a current collector disposed in a state being inelectrically contact with the active material-containing layer, themethod comprising: a granulating step of forming a composite particlecomprising an electrode active material, a conductive additive and abinder by bringing the conductive additive and the binder capable ofbinding the electrode active material and the conductive additive into aclose contact with the particle consisting of the electrode activematerial to integrate with each other; and a forming step of an activematerial-containing layer for forming the active material-containinglayer in a portion of the collector to be formed with the activematerial-containing layer using the composite particle, and thegranulating step comprising: a stock solution preparing step forpreparing a stock solution comprising the binder, the conductiveadditive and a solvent; a fluidized bed forming step for forming theparticle consisting of the electrode active material into a fluidizedbed by throwing the particle consisting of the electrode active materialinto a fluidizing bathe; and a spray-drying step, in which the stocksolution is sprayed into the fluidized bed comprising the particleconsisting of the electrode active material, thereby the stock solutionis allowed adhering to the particle consisting of the electrode activematerial and dried to remove the solvent from the stock solution adheredto the surface of the particle consisting of the electrode activematerial to bring the particle consisting of the electrode activematerial and the particle of the conductive additive into a closecontact with each other by means of the binder.
 63. The producing methodof an electrode according to claim 62, wherein, in the granulating step,the temperature in the fluidizing bathe is controlled to 50° C. or moreand melting point or less of the binder.
 64. The producing method of anelectrode according to claim 62, wherein, in the granulating step, theairflow generated within the fluidizing bathe is an airflow formed ofair, nitrogen gas, or inactive gas.
 65. The producing method of anelectrode according to claim 63, wherein the solvent comprised in thestock solution is capable of dissolving or dispersing the binder as wellas capable of dispersing the conductive additive.
 66. The producingmethod of an electrode according to claim 62, wherein a conductivepolymer is further dissolved in the stock solution.
 67. The producingmethod of an electrode according to claim 62, wherein a conductivepolymer is used as the binder.
 68. The producing method of an electrodeaccording to claim 66, wherein the conductive polymer has the ionconductivity.
 69. The producing method of an electrode according toclaim 62, wherein the forming step of the active material-containinglayer comprises: a sheet forming step in which sheet is formed bycarrying out a heat treatment and a pressure treatment on a fineparticle at least comprising the composite particle to obtain a sheetcomprising at least the composite particle; and a disposing step of theactive material-containing layer for disposing the sheet on thecollector as the active material-containing layer.
 70. The producingmethod of an electrode according to claim 62, wherein the forming stepof the active material-containing layer comprises: a coatingliquid-preparing step for preparing a coating liquid for forming anelectrode by adding the composite particle to a liquid capable ofdispersing or kneading the composite particle; a step for applying thecoating liquid for forming an electrode to a portion of the collector tobe formed with the active material-containing layer; and a step forsolidifying the liquid film of the coating liquid for forming anelectrode applied to a portion of the collector to be formed with theactive material-containing layer.
 71. The producing method of anelectrode according to claim 62, wherein, in the forming step of anactive material-containing layer, thickness T of the activematerial-containing layer and average particle diameter d of thecomposite particles comprised in the active material-containing layersatisfy the conditions expressed by following formulas (1) to (3):0.0005≦(T/d)≦1  (1)1 μm≦T≦150 μm  (2)1 μm≦d≦2000 μm  (3).
 72. A producing method of an electrochemicalelement provided with at least an anode, a cathode and an electrolytelayer having the ion conductivity, and having a structure such that theanode and the cathode are disposed opposite to each other beinginterposed by the electrolyte layer, an electrode produced in accordancewith the producing method of the electrode according to claim 62 beingused as the electrode for one or both of the anode and the cathode.